glossary of meteorology

This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.

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A

{{defn|Any {{gli|air current}} moving away from either the North Pole or the South Pole.}}

{{defn|The horizontal transport of some property of the {{gli|atmosphere}} or ocean, such as thermal energy, {{gli|humidity}}, or salinity. In the context of meteorology, the related term {{gli|atmospheric convection|convection}} generally refers to vertical transport.}}

{{defn|Describing a collection of low-lying, radially structured {{gli|clouds}} with distinct shapes (resembling leaves or wheels in satellite imagery), and typically organized in extensive {{gli|mesoscale convective system|mesoscale}} fields over marine environments. They are closely related to and sometimes considered a variant of {{gli|stratocumulus}} clouds.}}

{{defn|A scientific instrument used to measure the heating power of radiation, particularly {{gli|solar irradiance|solar radiation}}.}}

{{defn|A line drawn on a thermodynamic diagram along which an {{gli|air parcel}} moves as it ascends or descends through the atmosphere, {{gli|adiabatic cooling|cooling}} or {{gli|adiabatic heating|warming}} {{gli|adiabatic process|adiabatically}}; the path followed by this line depends on whether it is a {{gli|dry adiabat}} or a {{gli|saturated adiabat}}.}}

{{defn|An {{gli|adiabatic process}} of expansional cooling, in which a rising {{gli|air parcel}} decreases in {{gli|temperature}} as it increases in volume.}}

{{defn|An {{gli|adiabatic process}} of compressional warming, in which a sinking {{gli|air parcel}} increases in {{gli|temperature}} as it decreases in volume.}}

{{defn|The rate at which a {{gli|air parcel|parcel of air}} changes {{gli|temperature}} {{gli|adiabatic process|adiabatically}} as it moves vertically through the atmosphere. The parcel's {{gli|moisture content}} affects this rate: as it rises, a parcel saturated with moisture cools more slowly than a dry parcel because the release of latent heat at the phase change between gas and liquid acts to buffer the temperature decrease caused by the adiabatic expansion. When not otherwise qualified, the term most often refers to the {{gli|dry adiabatic lapse rate}}.}}

{{defn|Any idealized hypothetical process by which energy is transferred between a thermodynamic system and its surroundings only as work, without a corresponding transfer of heat or mass. Most compressible fluids, including gases in the {{gli|atmosphere}}, behave approximately adiabatically, such that meteorologists often use the assumption of adiabatic isolation when describing atmospheric systems. In such systems the {{gli|temperature}} of a {{gli|dry adiabat|dry}} {{gli|air parcel|parcel of air}} changes without any exchange of energy with its surroundings: as the parcel rises, the decrease in the surrounding {{gli|atmospheric pressure}} enables the air in the parcel to expand in volume, which decreases its internal energy and therefore its temperature ({{gli|adiabatic cooling|expansional cooling}}); as the parcel sinks and is compressed, its temperature increases ({{gli|adiabatic heating|compressional warming}}).}}

{{defn|The branch of biology that studies airborne organic particles, such as bacteria, viruses, fungal spores, pollen grains, and very small insects, which are passively transported by the air.}}

{{defn|The production of {{gli|weather map|weather charts}}.}}

{{defn|See {{gli|atmospheric science}}.}}

{{defn|The branch of meteorology that studies the upper regions of the Earth's or other planetary {{gli|atmosphere|atmospheres}}, specifically their atmospheric motions, chemical compositions and properties, and interactions with the other parts of the atmosphere and with space.}}

{{defn|A suspension of fine solid particles or liquid droplets in air or another gas. Examples of natural aerosols include {{gli|mist}}, {{gli|clouds}}, {{gli|fog}}, and dust.}}

{{defn|Any concentrated area of {{gli|winds}} that develops because of differences in pressure and/or temperature between adjacent {{gli|air parcels}}. They are generally divided into horizontal and vertical currents and exist at a variety of scales and in various layers of the atmosphere.}}

{{defn|A volume of air defined by its {{gli|temperature}} and {{gli|moisture content}}.}}

{{defn|In fluid dynamics, any amount of air that remains identifiable throughout its dynamic history while moving with an associated air flow.}}

{{defn|Any {{gli|thunderstorm}} that is generally weak and usually not {{gli|severe thunderstorm|severe}}. Such storms move relatively slowly, are short-lived, and often exist only as single cells (rather than in long continuous lines or complexes), but may still produce {{gli|lightning}} and heavy {{gli|rainfall}}. They derive their energy from {{gli|solar irradiance|solar radiation}} and commonly develop in temperate zones during {{gli|summer}} afternoons.}}

{{defn|Located in the atmosphere at some height (often significantly high) above the Earth's surface. The term is typically used to distinguish an {{gli|upper-air observation}} from a {{gli|surface weather observation}}, as in "winds aloft".}}

{{defn|A scientific instrument used to measure the altitude of an object (e.g. a {{gli|weather balloon}}) with respect to a fixed level such as sea level.}}

{{defn|A middle-altitude {{gli|cloud genus}} characterized by small globular masses, laminae, or rolls, white or gray in color, arranged in patches or extensive sheets at altitudes between {{convert|2|and|7|km|ft}}, with the individual elements being larger and more distinct than in {{gli|cirrocumulus}} but smaller than in {{gli|stratocumulus}}. Like other {{gli|stratocumuliform}} clouds, altocumulus usually signifies convection aloft. It is one of several classic "warning clouds" recorded by the aviation industry as a signal of developing {{gli|thunderstorms}}.}}

{{defn|A scientific and professional organization in the United States whose mission is to promote and disseminate information about the {{gli|atmospheric science|atmospheric}}, oceanic, and hydrologic sciences, and advance technologies, applications, and services related to them.}}

{{defn|A {{gli|wind}} that blows upslope from the low elevations of a valley to the higher elevations of surrounding hills or mountains as the result of daytime surface heating in the valley, usually at speeds of {{convert|12|knot|kph mph}} or less but occasionally at much higher speeds. Contrast {{gli|katabatic wind}}.}}

{{defn|A scientific instrument used to measure {{gli|wind speed}}.}}

{{defn|Any large-scale {{gli|air mass}} characterized by outward spiraling {{gli|winds}} which {{gli|atmospheric circulation|circulate}} around a strong center of {{gli|high-pressure area|high}} {{gli|atmospheric pressure}}. Surface-based anticyclones generally bring about cool, dry air and clear skies and are often implicated in weather phenomena such as {{gli|fog}} and {{gli|haze}}. Contrast {{gli|cyclone}}.}}

{{defn|Any {{gli|storm}} system involving an {{gli|anticyclone}}, in which {{gli|winds}} circulate around a region of {{gli|high-pressure area|high pressure}} in the direction opposite to that expected around a region of {{gli|low-pressure area|low pressure}}. Anticyclonic storms rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.}}

{{defn|The development or strengthening of an {{gli|anticyclonic rotation|anticyclonic circulation}} in the atmosphere, which may result in the formation or maintenance of a {{gli|high-pressure area}}. Contrast {{gli|cyclogenesis}}.}}

{{defn|A {{gli|wind}} generated by the local topography of a particular place; examples include {{gli|anabatic wind|anabatic winds}} and {{gli|katabatic wind|katabatic winds}}. Most such winds are {{gli|diurnal}} in character.}}

{{defn|See {{gli|heat index}}.}}

{{defn|A {{gli|tropical cyclone}} (locally known as a {{gli|hurricane}}) that forms in the Atlantic Ocean and achieves one-minute maximum {{gli|sustained winds}} exceeding {{cvt|74|mph|kph kn}}. Most of these storms occur between June 1 and November 30 each year, a time period referred to as the Atlantic hurricane season.}}

{{defn|See {{gli|evaporimeter}}.}}

{{defn|The various layers of gases surrounding the Earth and held in place by gravity. The Earth's atmosphere is the origin of the {{gli|weather}} phenomena studied in {{gli|meteorology}}. Atmospheric composition, {{gli|atmospheric temperature|temperature}}, and {{gli|atmospheric pressure|pressure}} vary across a series of distinct sublayers including the {{gli|troposphere}} and {{gli|stratosphere}}.}}

File:Atmosphere layers.jpg

{{defn|See {{gli|planetary boundary layer}}.}}

{{defn|The global-scale movement of {{gli|air masses}} within the Earth's {{gli|atmosphere}}. All meteorological phenomena are consequences of the atmospheric circulation, which manifests as a network of both latitudinal and longitudinal "cells" of convective activity; together with {{gli|ocean current|ocean circulation}}, these cells are the primary means by which thermal energy from the Sun is redistributed across the Earth's surface.}}

{{defn|The density (mass per unit volume) of the Earth's {{gli|atmosphere}}. Atmospheric density generally decreases proportionally with elevation above sea level, and also tends to vary with changes in {{gli|atmospheric pressure}}, {{gli|atmospheric temperature|temperature}}, and {{gli|humidity}}. According to the {{gli|International Standard Atmosphere}}, at a pressure of 1 atm and a temperature of 15° C, air has a density of approximately 1.225 kilograms per cubic metre (kg/m³), about {{frac|1000}} the density of liquid water.}}

{{defn|The pressure exerted by the Earth's {{gli|atmosphere}}. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of the air above the measurement point, and therefore decreases proportionally as altitude increases. The average atmospheric pressure at sea level on Earth is equal to approximately 1 standard atmosphere (atm), which is defined as exactly {{convert|101,325|Pa|mmHg|0}}.}}

{{defn|The collective of scientific disciplines that studies the Earth's {{gli|atmosphere}} and its processes, including the effects other systems have on the atmosphere and those the atmosphere has on other systems. {{gli|meteorology|Meteorology}} and {{gli|climatology}} are sub-disciplines.}}

{{defn|A measurement of the vertical distribution of physical properties through an {{gli|atmospheric}} column, usually including {{gli|atmospheric pressure|pressure}}, {{gli|temperature}}, {{gli|wind speed}} and {{gli|wind direction|direction}}, {{gli|moisture content}}, {{gli|ozone layer|ozone}} concentration, and pollution, among others.}}

{{defn|A measure of {{gli|temperature}} at one or more locations within the Earth's {{gli|atmosphere}}. Temperatures recorded in the atmosphere can vary widely with altitude, {{gli|humidity}}, and {{gli|solar irradiance}}, among other factors.}}

{{defn|A global-scale periodic oscillation of the Earth's {{gli|atmosphere}} caused by gravitational and thermal influences from the Sun and the Moon, analogous to oceanic tides.}}

{{defn|Any of the ranges of small bandwidths in the electromagnetic spectrum at which the Earth's {{gli|atmosphere}} is nearly transparent, i.e. where absorption by atmospheric gases is nearly zero and transmittance approaches unity both for incoming and outgoing radiation. Examples include the optical window from ~0.3 to 0.9 μm, the infrared window from ~8 to 13 μm, and the microwave window at wavelengths longer than ~1 mm. The existence of these windows is vital for the Earth–atmosphere system to be maintained near thermal equilibrium.}}

{{defn|A former message product of the U.S. {{gli|National Weather Service}} issued to provide information to pilots and aviation routes about {{gli|weather}} conditions across a large regional area within the United States. FAs were issued three times daily, valid for 18 hours, and covered an area the size of several states. They were replaced by Graphic Area Forecasts (GFAs) in 2017.}}

B

{{defn|A change of {{gli|wind direction}} in a counterclockwise fashion (e.g. northerly to northwesterly to westerly). Contrast {{gli|veering}}.}}

{{defn|The diffuse reflection of waves, particles, or signals back to the same direction from which they originated. Backscattering is the principle underlying all {{gli|weather radar}} systems, which can distinguish radar returns backscattered from target {{gli|aerosol|aerosols}} such as raindrops and snowflakes because the strength of the returns depends largely on the size and reflectivity of the targets.}}

{{defn|Any segment of a larger geographic region that typically experiences warmer temperatures than the region as a whole, especially during the local winter season, which may prove favorable for agriculture.}}

{{defn|A scientific instrument used to measure and continuously record changes in {{gli|atmospheric pressure}} over time.}}

{{defn|A measure of the misalignment between a pressure gradient and a density gradient in a stratified fluid such as the {{gli|atmosphere}}. In the context of meteorology, a baroclinic atmosphere is one in which {{gli|atmospheric density}} depends on both {{gli|temperature}} and {{gli|atmospheric pressure|pressure}}, in contrast to a {{gli|barotropity|barotropic}} atmosphere, in which density depends only on pressure. Areas of high atmospheric baroclinity are generally found in the temperate and polar latitudes and are characterized by the frequent formation of {{gli|cyclone|cyclones}}.}}

{{defn|The close alignment between a pressure gradient and a density gradient in a stratified fluid such as the {{gli|atmosphere}}. In the context of meteorology, a barotropic atmosphere is one in which {{gli|atmospheric density}} depends only on {{gli|atmospheric pressure|pressure}} and is more or less independent of {{gli|temperature}}, in contrast to a {{gli|baroclinity|baroclinic}} atmosphere. Unlike liquids, gaseous fluids such as the air in the atmosphere are generally not barotropic, but the assumption of barotropity can nonetheless be useful in modeling fluid behavior. Tropical latitudes are more nearly barotropic than the mid-latitudes because air temperature is more nearly horizontally uniform in the tropics.}}

{{defn|A scientific instrument used to measure {{gli|atmospheric pressure}}. The two most common types are mercury barometers and aneroid barometers.}}

{{defn|See {{gli|atmospheric pressure}}.}}

{{defn|A low-level core of high {{gli|wind speed|wind speeds}} that sometimes occurs at altitudes of {{convert|1000|–|1500|m|ft}} in the vicinity of a mountain range, as a consequence of the deceleration of an {{gli|air current|airflow}} as it crosses a major topographic barrier and releases latent heat which changes the local thermodynamics of the flow.}}

{{defn|A principle of fluid dynamics which states that an increase in the speed of a moving fluid occurs simultaneously with a decrease in the pressure exerted by the fluid or in the fluid's potential energy.}}

{{ghat|Also {{gli|clear ice}}.}}

{{defn|A thin, nearly transparent coating of {{gli|glaze|glaze ice}} on a solid surface, especially a road or walkway, which because of its transparency is often practically invisible and therefore presents a significant hazard to drivers and pedestrians.}}

{{defn|A severe {{gli|snowstorm}} characterized by strong {{gli|sustained winds}} of at least {{cvt|35|mph|kph}} and {{gli|blowing snow}}, typically lasting three hours or more. They can have an immense size, covering hundreds or thousands of square miles, and occur most often in temperate, polar, or mountainous regions during the {{gli|winter}}.}}

{{defn|A nearly stationary pattern in the {{gli|atmospheric pressure}} field overlying a large geographic area, which effectively "blocks" or diverts the movements of {{gli|cyclone|cyclones}} and other convective systems. These blocks can remain in place for days or weeks, causing the areas affected by them to experience the same kind of weather for extended periods of time.}}

{{defn|A {{gli|lithometeor}} phenomenon that occurs when particles of dust are lifted from the Earth's surface by {{gli|wind}} and blown about in clouds or sheets. It is classified as an obstruction to vision in {{gli|METAR}} aviation weather observations and is commonly reported if the amount of suspended dust reduces horizontal {{gli|visibility}} to {{convert|6|mi|km|order=flip|0}} or less. Extreme cases may be called {{gli|dust storms}}.}}

{{defn|A {{gli|lithometeor}} phenomenon that occurs when grains of sand are lifted from the Earth's surface by {{gli|wind}} and blown about in clouds or sheets. It is classified as an obstruction to vision in {{gli|METAR}} aviation weather observations and is commonly reported if the amount of suspended sand reduces horizontal {{gli|visibility}} to {{convert|6|mi|km|order=flip|0}} or less. Extreme cases may be called {{gli|sandstorm|sandstorms}}.}}

{{defn|{{gli|snow|Snow}} blown about by {{gli|wind}}, either from falling snow or snow lifted from the surface, to a height of at least {{convert|2|m|ft}}, reducing {{gli|visibility}}. It is a defining characteristic of {{gli|blizzards}}.}}

{{defn|A characteristic radar return from a {{gli|mesoscale convective system}} that is shaped like an archer's bow and usually associated with {{gli|squall line|squall lines}} or lines of convective {{gli|thunderstorms}}. The distinct bow shape is a result of the focusing of a strong flow at the rear of the system. Especially strong bow echoes may develop into {{gli|derecho|derechos}}.}}

File:Bow Echo Kansas City.jpg

{{defn|no=1|Any generally light {{gli|wind}}.}}

{{defn|no=2|Any local-scale air movement that is {{gli|atmospheric convection|convectively}} forced, e.g. a {{gli|land breeze}} or {{gli|sea breeze}}.}}

{{defn|no=3|On the {{gli|Beaufort scale}}, a {{gli|wind speed}} of force numbers 2 to 6, ranging from {{convert|4|–|27|kn|kph mph|0}}, and categorized as follows: light breeze, 4–6 knots; gentle breeze, 7–10 knots; moderate breeze, 11–16 knots; fresh breeze, 17–21 knots; and strong breeze, 22–27 knots.}}

{{defn|A dimensionless ratio related to the consumption of {{gli|turbulence}} divided by the shear production of turbulence (the generation of kinetic energy caused by {{gli|wind shear}}). It is an approximation of the Gradient Richardson Number.}}

{{defn|See {{gli|wildfire}}.}}

C

{{defn|A state of the atmosphere in which there is virtually no horizontal motion of the air. It corresponds to force number 0 on the {{gli|Beaufort scale}}, with a {{gli|wind speed}} less than {{cvt|1|kn|kph}}. Calm conditions are common in the {{gli|subtropical high-pressure belt|subtropical high-pressure belts}} and in the {{gli|doldrums}}.}}

{{term|Canadian Meteorological and Oceanographic Society (CMOS)}}

{{defn|The national society of individuals and organizations dedicated to advancing atmospheric and oceanic sciences and related environmental disciplines in Canada, officially constituted in 1967.}}

{{defn|Provides forecast guidance to national and regional prediction centres in Canada.}}

{{defn|See {{gli|Nor'west arch}}.}}

{{defn|An approximately stationary {{gli|cloud}} on or hovering above an isolated mountain peak. See also {{gli|pileus}} and {{gli|lenticular cloud}}.}}

{{defn|The ability of a {{gli|wind}} current to transport material, as measured by the maximum amount of detritus (e.g. silt, sand, and/or gravel) carried past a specific point per unit time. Capacity increases with {{gli|wind speed}} and decreases as the particle size of the detrital debris increases.}}

{{defn|A {{gli|cloud species}} that displays at least in its upper part {{gli|cumulus|cumuliform}} protuberances resembling the turrets of a castle, giving a crenellated aspect.}}

{{defn|See {{gli|katabatic wind}}.}}

{{defn|A measure of the height above the Earth's surface of the base of the lowest layer of {{gli|clouds}} or obscuring phenomena that covers more than half of the sky (more than four {{gli|okta|oktas}}). An "unlimited" ceiling means either that the sky is mostly free of {{gli|cloud cover}} or that the clouds are sufficiently high so as not to impede aircraft operation by {{gli|visual flight rules}}.}}

{{defn|A type of {{gli|weather balloon}} used by meteorologists to determine the height of the {{gli|cloud base}} {{gli|height above ground level|above ground level}} during daylight hours by measuring the time it takes for the balloon, released from the ground and rising at a known rate of ascent, to begin to disappear into the clouds.}}

{{defn|A type of {{gli|height above ground level|cloud-height}} indicator that uses a searchlight to project a beam of light vertically onto a {{gli|cloud base}} (similar to a {{gli|ceilometer}}), with the height of the illuminated spot then calculated by the observer using a clinometer or alidade.{{cite book |last1=Middleton |first1=W. E. K. |title=Invention of the Meteorological Instruments |date=1969 |publisher=Johns Hopkins Press |location=Baltimore |page=274}}}}

{{defn|An instrument that uses a laser transmitter or other light source and a collocated receiver to determine the {{gli|height above ground level|height}} of a {{gli|ceiling|cloud ceiling}} or {{gli|cloud base}} overhead, or to measure the concentration of {{gli|aerosol|aerosols}} within the atmosphere.}}

{{defn|no=1|Any {{gli|atmospheric circulation}} feature that is more or less closed, occurring at any of number of scales, including massive latitudinally oriented circulations such as {{gli|Hadley cell|Hadley cells}}; {{gli|mesoscale meteorology|mesoscale}} motions that characterize {{gli|cellular convection}} and cause the formation of {{gli|cellular cloud|cellular clouds}}; and {{gli|storm cell|storm cells}} formed by {{gli|updraft}} and/or {{gli|downdraft}} loops within a {{gli|thunderstorm}}.}}

{{defn|no=2|In {{gli|weather radar}}, a local maximum in radar reflectivity that undergoes a life cycle of growth and decay, and which often displays an identifiable structure in radar returns. Cells in ordinary convective thunderstorms typically last 20 to 30 minutes, but may form longer-lasting {{gli|multicellular thunderstorm|multicell storms}} or {{gli|supercell|supercells}}.}}

{{defn|A {{gli|mesoscale meteorology|mesoscale}} organization of {{gli|cellular convection|convective activity}} in the form of a quasi-regular pattern of {{gli|clouds}} behaving as individual {{gli|cell|convective cells}}, often stretching horizontally for tens of kilometers. Such patterns may be composed of open or closed cells or both: the open cells consisting of a ring of {{gli|cumulus}} with a clear center, and the closed cells filled with {{gli|stratocumulus}} surrounded by a clear rim.}}

{{defn|Develops techniques for computer-based prediction of high-impact local weather, such as individual spring and winter storms, using Doppler weather radar and other sources. Based in Oklahoma, United States.}}

{{defn|The large, centralized, contiguous area of {{gli|thunderstorms}} surrounding the rotational center of a strong {{gli|tropical cyclone|tropical}} or {{gli|subtropical cyclone}}. When a cyclone reaches sufficient intensity, a distinguishable {{gli|eye}} may develop within the CDO. The strongest winds and heaviest rainfall are usually found beneath the coldest cloud tops in the CDO.}}

{{defn|The {{gli|atmospheric pressure}} at the center of a recognizable {{gli|high-pressure area|high}} or {{gli|low-pressure area}} at any given instant, i.e. the highest pressure in a high or the lowest pressure in a low.}}

{{defn|An instrument used for counting the number of {{gli|lightning}} discharges within a specific radius.}}

{{defn|A warm, dry {{gli|föhn}} wind formed by a rainstorm dropping its precipitation onto the windward side of a mountain, thus drying the air mass before it blows across the leeward side, drops in elevation, and warms by {{gli|adiabatic heating}}. Common in the northwestern United States and southwestern Canada, a chinook can cause temperatures to rise from {{convert|-48|C|1}} to {{convert|9|C|1}} in 24 hours, an increase of {{convert|57|C-change|F-change}}.}}

{{defn|Common short form of {{gli|atmospheric circulation}}.}}

{{defn|A {{gli|cloud type|genus}} of {{gli|cloud}} with both {{gli|stratiform}} and {{gli|cumuliform}} characteristics, signifying {{gli|atmospheric convection}}, and appearing as white, patchy, transient sheets of ripples or tufts organized in undulating rows, usually between {{cvt|5|and|12|km|ft}} above sea level. Though composed mainly of ice crystals, cirrocumulus is distinguished from {{gli|cirrus}} and {{gli|cirrostratus}} by the presence of small amounts of supercooled liquid water droplets.}}

{{defn|A {{gli|cloud type|genus}} of {{gli|cloud}} characterized by thin, wispy, feather-like strands that appear white or light grey in color and form at very high altitudes, usually between {{cvt|5|and|13.7|km|ft}} above sea level. Cirrus clouds often develop from the {{gli|outflow}} of {{gli|cumulonimbus}} clouds in advance of {{gli|fronts}} or {{gli|thunderstorms}}, and therefore may indicate the imminent arrival of {{gli|precipitation}}.}}

{{defn|A type of solid {{gli|precipitation}} which forms when relatively large drops of water are supercooled into a dense, transparent coating of {{gli|ice}} without air or other impurities. It is similar to {{gli|glaze}} and {{gli|hard rime}} and, when formed on the ground, is often called {{gli|black ice}}.}}

{{defn|The statistics of {{gli|weather}} in a given region over long periods of time, measured by assessing long-term patterns of variation in {{gli|temperature}}, {{gli|atmospheric pressure}}, {{gli|humidity}}, {{gli|wind}}, {{gli|precipitation}}, and other {{gli|meteorology|meteorological}} variables. The climate of a particular location is generated by the interactions of the {{gli|atmosphere}}, {{gli|hydrosphere}}, cryosphere, lithosphere, and biosphere and strongly influenced by latitude, altitude, and local topography. Climates are often classified according to the averages or typical ranges of different variables, most commonly temperature and precipitation.}}

{{defn|A branch of the {{gli|atmospheric science|atmospheric sciences}} that studies {{gli|climate}}, defined as {{gli|weather}} conditions averaged over an extended to indefinite period of time. Climatology incorporates aspects of oceanography, geology, biogeochemistry, and the related field of {{gli|meteorology}} to understand the long-term dynamics of climate-influencing phenomena and to produce climate models which can be used to estimate {{gli|paleoclimatology|past climates}} and predict future climates.}}

{{defn|An {{gli|aerosol}} consisting of a visible mass of minute liquid droplets, frozen crystals or other particles suspended in the {{gli|atmosphere}}. Water or various other chemicals may compose the droplets and crystals. On Earth, clouds are formed as a result of the saturation of an {{gli|air mass}} when it is cooled to its {{gli|dew point}} or when it gains sufficient moisture (usually in the form of {{gli|water vapor}}) from an adjacent source to raise the dew point to the ambient temperature. There are many different types of clouds, which are classified and named according to their shape and altitude.}}

{{defn|A pictorial key to the classification and nomenclature of {{gli|clouds}}.}}

{{defn|The lowest altitude of the visible portion of a {{gli|cloud}}.}}

{{defn|See {{gli|fogbow}}.}}

{{defn|The obscuration of all or part of the {{gli|sky}} by {{gli|clouds}} as observed from a particular location, or the specific fraction of the sky obscured by clouds as measured in {{gli|okta|oktas}}.}}

{{defn|See {{gli|cloud type}}.}}

{{defn|A type of {{gli|photometeor}} consisting of colorful iridescent patterns appearing most commonly near the semi-transparent edges of thin {{gli|clouds}} such as {{gli|cirrus}} and {{gli|altocumulus}} that are in the general proximity of the Sun or Moon. They are caused by the diffraction of sunlight or moonlight by thin, uniform layers of very small water droplets or {{gli|ice crystal|ice crystals}}.}}

{{defn|Any of a set of 14 Latin terms used to describe the shape and internal structure of {{gli|troposphere|tropospheric}} {{gli|clouds}}. Cloud species are subdivisions of {{gli|cloud type|cloud genera}} and are themselves further subdivided into {{gli|cloud variety|cloud varieties}}.}}

{{defn|Any of a set of Latin names used to classify and identify {{gli|clouds}} occurring in the {{gli|troposphere}}, typically by characteristics such as their altitude, shape, and convective activity. A set of 10 or 12 traditional cloud types defined by the {{gli|World Meteorological Organization}} and further subdivided into {{gli|cloud species}} and {{gli|cloud variety|cloud varieties}} is widely used in meteorology. Other classification systems have proposed many additional types.}}

{{defn|A colloquial term used to describe an excessive {{gli|precipitation}} event, characterized by brief, sudden, exceptionally heavy {{gli|rain}} and/or {{gli|hail}} falling from a {{gli|cloud}}, typically as part of a {{gli|thunderstorm}} associated with violent upward and downward convective currents.}}

{{defn|The point of intersection of a {{gli|trough}} and a {{gli|ridge}} in the pressure pattern of a {{gli|weather map}}. It generally takes the shape of a saddle in which the air pressure is slightly higher than that within the low-pressure regions but still lower than that within the {{gli|anticyclone|anticyclonic zones}}.}}

{{defn|A type of {{gli|front}} located at the leading edge of a cooler {{gli|air mass}} as it replaces a warmer air mass. Cold fronts lie within a sharp surface {{gli|trough}} of {{gli|low-pressure area|low pressure}} and the temperature difference between the air masses they separate can exceed {{convert|30|C|F}}. When enough moisture or instability is present, lines of {{gli|rain}} or {{gli|thunderstorms}} may accompany the boundary as it moves. In {{gli|surface weather analysis}}, cold fronts are symbolized by a blue line with triangles pointing in the direction of travel.}}

{{defn|A period of weather characterized by excessively low temperatures, which may or may not also be accompanied by changes in {{gli|humidity}}. Very cold weather is often only referred to as a cold wave if the temperature, or the rate at which the temperature decreases within a given time period, is abnormal relative to the typical climate for a given location during a given season. Contrast {{gli|heat wave}}.}}

{{defn|A type of {{gli|low-pressure area}} that forms in southeastern Colorado or northeastern New Mexico, in the United States, and then proceeds to move east across the Great Plains, often producing heavy {{gli|snow}} and {{gli|ice}} when occurring in the winter.}}

{{defn|See {{gli|atmospheric convection}}.}}

{{defn|The inability of an {{gli|air mass}} to resist vertical motion. In a stable atmosphere vertical movement of air is generally difficult, whereas in an unstable atmosphere vertical disturbances can be quite exaggerated, resulting in {{gli|turbulence|turbulent}} airflow and {{gli|atmospheric convection|convective activity}} that may lead to extensive vertical clouds, {{gli|storms}}, and {{gli|severe weather}}.}}

{{defn|A pattern of fluid flow that brings about a net inflow of fluid elements into a region, in either the atmosphere or the ocean, accompanied by compensating vertical motion. When convergence occurs in the lower atmosphere, generally below about {{convert|550|hPa|atm}}, the compensatory air motion is upward, with inflow gradually changing to {{gli|outflow}} at higher altitudes; when it occurs in the upper atmosphere, the air motion is downward, with {{gli|divergence}} near the surface.{{cite book |editor1-last=Smith |editor1-first=Jacqueline |title=The Facts on File Dictionary of Weather and Climate |date=2001 |publisher=Facts on File |location=New York |isbn=9780816045327 |ol=11359575M |url=https://openlibrary.org/books/OL11359575M/The_Facts_on_File_Dictionary_of_Weather_and_Climate_%28The_Facts_on_File_Science_Dictionaries%29}}}}

{{defn|An optical phenomenon consisting of apparent concentric, pastel-colored rings around a bright celestial object (such as the Sun or the Moon), which are produced by the diffraction of light by individual water droplets or sometimes small {{gli|ice crystal|ice crystals}} in a cloud or on a foggy glass surface. Coronae differ from {{gli|halo|halos}} in that the latter are formed by refraction from comparatively large particles.}}

{{defn|Any {{gli|wind}} that moves in a direction that is perpendicular to the direction of travel of a reference object, such as an airplane.}}

{{defn|An inviscid line-vortex instability most commonly observed in the skies behind large aircraft such as the Boeing 747. It occurs when the wingtip vortices interact with contrails from the engines, producing characteristic visual distortions in the shapes of the contrails.}}

{{defn|Of or relating to heaped, "puffy" {{gli|clouds}}, such as {{gli|cumulus}} or {{gli|cumulonimbus}}, that form as a result of {{gli|atmospheric convection}}.}}

{{defn|A {{gli|cloud type|genus}} of {{gli|cloud}} characterized by low-level "puffy" or "cotton-like" forms with flat bases (generally opaque white in color but sometimes with grey undersides), which occur individually or multiply in a variety of distinct subforms, usually at altitudes less than {{cvt|2|km|ft}} above sea level. Cumulus clouds normally produce little or no {{gli|precipitation}}, but can develop into precipitation-bearing clouds such as {{gli|cumulonimbus}} when influenced by atmospheric instability, moisture, and temperature gradients.}}

{{defn|Any large-scale {{gli|air mass}} characterized by inward spiraling {{gli|winds}} which {{gli|atmospheric circulation|circulate}} around a strong center of {{gli|low-pressure area|low}} {{gli|atmospheric pressure}}. Cyclones can {{gli|cyclogenesis|form}} over land or water, can vary in size from {{gli|mesocyclone|mesocyclones}} such as {{gli|tornadoes}} to {{gli|synoptic scale meteorology|synoptic-scale}} phenomena such as {{gli|tropical cyclones}} and {{gli|polar vortex|polar vortices}}, and may transition between tropical, subtropical, and {{gli|extratropical cyclone|extratropical}} phases. Contrast {{gli|anticyclone}}.}}

File:Low pressure system over Iceland.jpg

{{defn|The development or strengthening of a {{gli|cyclonic rotation|cyclonic circulation}} in the atmosphere. Cyclogenesis may refer to a number of different processes that occur under a variety of conditions and at a variety of scales, all of which result in the formation of some sort of {{gli|cyclone}}; for instance, {{gli|tornadoes}} are a type of {{gli|mesocyclone}} whose development may be variously described as cyclogenesis or, more specifically, {{gli|tornadogenesis}}. Contrast {{gli|anticyclogenesis}}.}}

D

{{defn|A type of specialized eyewear used by meteorologists and astronomers for adapting the eyes to the dark prior to an observation made at night, or for aiding with identification of {{gli|clouds}} during bright sunshine or when there is a glare from snow.}}

{{defn|The first appearance of sunlight in the eastern {{gli|sky}} before sunrise, or the time that marks the beginning of the morning {{gli|twilight}}.{{cite book |editor1-last=Geer |editor1-first=Ira W. |title=Glossary of Weather and Climate, with Related Oceanic and Hydrologic Terms |date=1996 |publisher=American Meteorological Society |location=Boston, Mass. |isbn=1878220195 |url=https://openlibrary.org/works/OL19426397W/Glossary_of_weather_and_climate?edition=glossaryofweathe0000unse}}}}

{{defn|The period of the day between sunrise and sunset, during which any given point on the Earth experiences natural illumination from especially direct sunlight, known as daylight.}}

{{defn|See {{gli|tornado debris signature}}.}}

{{defn|A decrease in the {{gli|central pressure|central}} and surrounding sea-level {{gli|atmospheric pressure|pressure}} within the circulation of a pressure system (usually a {{gli|low-pressure area|low-pressure system}}) over a short period of time, with the result that mass is exported from the total air column overlying the system faster than it is supplied. Deepening of a low is commonly accompanied by the intensification of its {{gli|cyclonic rotation|cyclonic circulation}} and hence its {{gli|winds}}, and the term is frequently used to imply {{gli|cyclogenesis}}. Contrast {{gli|filling}}.}}

{{defn|The rate of change of shape of a fluid body such as an {{gli|air mass}}. This quantity is very important in the formation of {{gli|weather front|atmospheric fronts}}, in the explanation of {{gli|cloud}} shapes, and in the diffusion of materials and properties through the atmosphere.}}

{{defn|A measure of the difference between the mean daily temperature and a specified reference temperature for a given day. For a specified period, e.g. a month or a year, the number of degree-days is the sum of all degree-days within that period.}}

{{defn|An advisory issued by the U.S. {{gli|National Weather Service}} to caution the public about the possibility that horizontal {{gli|visibility}} may be reduced by dense {{gli|fog}} to {{convert|0.25|mi|km}} or less.}}

{{defn|Any {{gli|low-pressure area|area of low atmospheric pressure}} at a given level in the atmosphere; i.e. a "low" or {{gli|trough}}. The term is used especially frequently to refer to an early stage in the development of a {{gli|tropical cyclone}} during which the disturbance is only weakly developed or poorly organized; see {{gli|tropical depression}}.}}

{{defn|A type of storm that produces widespread, straight-lined {{gli|sustained winds}} that are associated with {{gli|severe thunderstorms}}.}}

{{defn|Liquid water droplets that commonly appear on thin, exposed surfaces in the morning or evening due to the condensation of atmospheric {{gli|moisture}} on radiatively cooled surfaces. When temperatures are low enough, the water droplets freeze into ice particles known as {{gli|frost}}.}}

{{defn|The {{gli|temperature}} to which an {{gli|air parcel}} must be cooled, at constant {{gli|atmospheric pressure|pressure}} and {{gli|moisture content}}, in order for saturation to occur. Continued cooling below the dew point will cause condensation of water droplets if atmospheric conditions are favorable. Dew point is often used as a proxy by which to indicate the moisture content of the air.}}

{{term|term=dew point depression|content=dew point depression (T–T_d)}}

{{defn|The difference between the actual {{gli|temperature}} and the {{gli|dew point}} at a certain altitude in the atmosphere. A small dew point depression indicates more moisture and higher {{gli|relative humidity}}, which in the lower {{gli|troposphere}} can result in low {{gli|cloud base|cloud bases}} and {{gli|lifted condensation level|lifted condensation levels}}, which are important factors contributing to the development of {{gli|severe thunderstorms}}.}}

{{defn|Any thermodynamic process in which the {{gli|temperature}} of an {{gli|air parcel}} changes as a result of the transfer of energy (e.g. heat) between the parcel and its surroundings, as opposed to an {{gli|adiabatic process}}, in which the temperature changes without any such exchange. Most thermodynamic processes near the Earth's surface are diabatic, owing to the continual mixing of air and {{gli|turbulence}}.}}

{{defn|A ground-level {{gli|cloud}} composed of tiny {{gli|ice}} crystals. Because it generally forms in sub-freezing temperatures beneath otherwise clear or nearly clear skies, diamond dust is sometimes referred to as clear-sky precipitation.}}

{{defn|The elongation of a fluid body, such as an {{gli|air mass}}, normal to the flow (streamline divergence). It is a flow pattern of {{gli|deformation}}.}}

{{defn|The component of incoming {{gli|solar irradiance|solar radiation}} that is scattered from the direct solar beam by molecules of air, {{gli|aerosol|aerosols}}, {{gli|clouds}}, or particulate matter in the {{gli|atmosphere}} and subsequently reaches the Earth's surface in nearly equal amounts from nearly all parts of the sky during {{gli|daytime|daylight}}.}}

{{defn|A closed, vertically distributed thermal circulation in the atmosphere, in which warm, lighter air rises and cold, denser air sinks (or, equivalently, a system in which the rising motion occurs at a higher {{gli|potential temperature}} than the sinking motion). Such a {{gli|cell}} converts heat energy to potential energy and then to kinetic energy. Contrast {{gli|indirect circulation}}.}}

{{defn|A horizontal zone across which temperature, humidity, wind speed, or any other meteorological variable changes abruptly, such as a {{gli|front}}.}}

{{defn|A scientific instrument used to measure the {{gli|raindrop size distribution|size distribution}} and velocity of falling {{gli|hydrometeor|hydrometeors}} such as {{gli|rain|raindrops}}.}}

{{defn|Occurring or varying in the course of a solar day (i.e. daily; completed within and recurring every 24 hours), or during the local {{gli|daytime}}.}}

{{defn|The range between the maximum and minimum values of a meteorological quantity (e.g. temperature, pressure, relative humidity) observed during the course of a solar day.}}

{{defn|A unit of measurement used to describe the quantity of a trace gas (primarily atmospheric {{gli|ozone}} concentrations) present in a {{gli|atmospheric sounding|vertical column}} of the atmosphere. It is defined as the thickness (in units equivalent to 10 μm) of the layer of pure gas which would be formed if all of the gas molecules in the column could be collected on the surface at standard temperature and pressure.}}

{{defn|See {{gli|Intertropical Convergence Zone}}.}}

{{defn|A surface-level {{gli|wind}} system that emanates from an elevated point source and blows radially in all directions upon making contact with the ground. Downbursts are created when {{gli|rain}}-cooled air descends rapidly, and can produce very strong damaging winds. They are often confused with {{gli|tornadoes}}, although a tornado causes air to move inward and upward whereas a downburst directs it downward and outward. {{gli|microburst|Microbursts}}, {{gli|macrobursts}}, and {{gli|heat bursts}} are all types of downburst.}}

{{defn|Particles of {{gli|snow}} lifted by the {{gli|wind}} to a modest height, generally less than {{convert|1.8|m|ft|0}} above the ground. Drifting snow does not significantly reduce {{gli|visibility}} at eye level below {{convert|10|km|mi}}, in contrast to {{gli|blowing snow}}.}}

{{defn|A type of light {{gli|precipitation}} consisting of liquid water droplets which are smaller than ordinary {{gli|rain|raindrops}}, generally less than {{convert|0.05|mm|in|3}} in diameter and falling at a rate of less than {{convert|1|mm|in|2}} per day.}}

{{defn|Any prolonged period of below-average {{gli|precipitation}} in a given region that results in shortages in the local water supply, whether of atmospheric, surface water, or ground water. Droughts can last for months or even years, and may be declared after as few as 15 days; annual or seasonal decreases in precipitation, such as {{gli|dry season|dry seasons}} in the tropics, are sometimes called droughts, though a true drought is by definition abnormal or irregular. Drought conditions result from the confluence of a wide variety of climatic factors and may be exacerbated by {{gli|heat wave|hot temperatures}}; in turn, droughts may increase the likelihood of {{gli|wildfire|wildfires}}.}}

{{defn|{{gli|Lightning}} associated with a {{gli|dry thunderstorm}}.}}

{{defn|Meteorological slang for a {{gli|synoptic scale meteorology|synoptic-scale}} or {{gli|mesoscale meteorology|mesoscale}} weather process. A dry punch that occurs near the Earth's surface may result in a {{gli|dry line}} bulge, whereas a dry punch aloft may increase the potential for {{gli|severe thunderstorms}}.}}

{{defn|An annual period of relatively low or infrequent {{gli|precipitation}}, during which weather patterns are typically dominated by lengthy periods of {{gli|high-pressure area|high atmospheric pressure}}, high temperatures, and low {{gli|humidity}}. The term is primarily used in the {{gli|tropics}}, in contrast to the {{gli|wet season}}.}}

{{defn|A {{gli|thunderstorm}} that produces {{gli|thunder}} and {{gli|lightning}} but in which most or all of its {{gli|precipitation}} evaporates before reaching the ground. Dry thunderstorms occur necessarily in dry conditions, and their {{gli|lightning strike|lightning strikes}}, sometimes referred to as dry lightning, are a major cause of {{gli|wildfire|wildfires}}.}}

{{defn|A meteorological phenomenon characterized by very strong winds that blow dust-filled air over an extensive area. Dust storms arise when a {{gli|outflow boundary|gust front}} or other strong wind blows loose dirt, sand, and/or small rocks from a dry surface into the atmosphere, drastically reducing visibility. Though the term is sometimes restricted to storms occurring over normally arable land suffering from {{gli|drought}}, it is also used interchangeably with {{gli|sandstorm}} and {{gli|haboob}}.}}

E

{{defn|On a radar display, the appearance of the radio signal that is scattered or reflected back from a target. The distinct characteristics of a radar echo can be used to identify the distance and velocity of the target with respect to the signal source as well as the target's size, shape, and composition.}}

{{defn|The swirling motion of a fluid and the reverse current created when the flow regime experiences {{gli|turbulence}}, such as when an obstacle blocks part of the path of flow.}}

{{defn|The layer in a fluid in which there is a force balance between the pressure-gradient force, the Coriolis force, and turbulent drag. Ekman layers occur in both the {{gli|atmosphere}} and the ocean.}}

{{defn|The warm phase of the {{gli|El Niño–Southern Oscillation}} (ENSO), associated with the annual development of a band of warm ocean water in the eastern equatorial Pacific, which brings {{gli|low-pressure area|low pressure}} and heavy {{gli|rainfall}} to the coasts of Central and South America. The El Niño phase of the cycle may last between two and seven years, with local weather patterns recurring every year. The cool phase of the ENSO is called {{gli|La Niña}}.}}

{{defn|An irregular long-term periodic variation in {{gli|winds}} and {{gli|sea surface temperature|sea surface temperatures}} over the tropical eastern Pacific Ocean which affects the climate of most of the world but especially the tropics and subtropics in a cycle lasting years or decades. The phenomenon, a consequence of the {{gli|Walker circulation}}, is marked by two phases: a warming phase, {{gli|El Niño}}, during which sea temperatures are above average over a large part of the eastern Pacific Ocean, driving high pressure and dry weather in Asia and low pressure and heavy precipitation in the Americas; and a cooling phase, {{gli|La Niña}}, during which sea temperatures are below average in the eastern Pacific and the reverse weather pattern occurs. Each phase can last for several years, with local seasonal weather patterns recurring predictably, though there are also long intervals of "neutral" or average conditions when neither El Niño nor La Niña is active.}}

{{defn|Any visible or audible indicator of atmospheric electricity, including all types of {{gli|lightning}} discharges, {{gli|thunder}}, and {{gli|aurorae}}.}}

{{defn|One of four thermodynamic diagrams used to display temperature {{gli|lapse rate}} and {{gli|moisture content}} profiles in the atmosphere. Emagrams have axes of {{gli|temperature}} (T) and {{gli|atmospheric pressure|pressure}} (p). Temperature and {{gli|dew point}} data from {{gli|radiosondes}} are plotted on these diagrams to allow calculations of convective stability or {{gli|convective available potential energy}}.}}

{{defn|A {{gli|weather forecasting}} technique in which a {{gli|numerical weather prediction|numerical weather model}} generates a set of multiple (often several dozen) forecasts, each based on a slightly different set of initial atmospheric conditions, intended to provide an indication of the range of possible future states of the atmosphere. If the forecasts are consistent, they are usually considered reliable; if they diverge, meteorologists may feel less confident in making specific predictions for the forecast area.}}

{{defn|The process by which the air surrounding a developing {{gli|cloud}} is mixed into an ascending {{gli|convection current}} within the cloud, which has the effect of reducing the current's buoyancy. If very dry air is introduced, evaporation of the cloud droplets may cause the cloud system to dissipate completely.}}

{{defn|The actual rate at which atmospheric {{gli|temperature}} changes with {{gli|altitude}}, as measured by a {{gli|radiosonde}}; this is in contrast to the rate predicted by the theoretical {{gli|process lapse rate}}. On average, the temperature of the {{gli|troposphere}} decreases with height at a rate of {{convert|6.5|C-change|F-change}} per kilometre, but this rate is influenced by many factors. In general, the ELR is lower nearer to the ground surface, during the local {{gli|winter}}, and over continental landmasses.}}

{{defn|The predecessor agency (1965–1970) to the {{gli|National Oceanic and Atmospheric Administration}} (1970–present).}}

{{defn|The {{gli|temperature}} obtained when an {{gli|air parcel}} expands {{gli|adiabatic heating|adiabatically}}, at constant pressure, until its water vapor content has been condensed out and the latent heat of condensation is available to raise the air temperature.}}

{{defn|An instrument used to measure the rate of evaporation of water into the atmosphere. The most basic design consists of an open, ground-level evaporation pan from which water is allowed to evaporate freely.}}

{{defn|Any {{gli|weather}} that is unexpected, unusual, unpredictable, unseasonal, or especially {{gli|severe weather|severe}} (i.e. weather at the extremes of an historical distribution).}}

{{defn|A typically circular region at the center of a strong {{gli|tropical cyclone}} that is the location of the storm's lowest {{gli|atmospheric pressure|barometric pressure}}. The eye is usually characterized by light winds, clear skies, and mostly calm weather, in stark contrast to the severe weather that occurs in the surrounding {{gli|eyewall}} and the rest of the storm.}}

{{defn|A nautical term used to describe the direction from which the {{gli|wind}} is blowing.}}

F

{{defn|See {{gli|katabatic wind}}.}}

{{defn|The length of water over which a given {{gli|wind}} blows. Fetch length and {{gli|wind speed}} together determine the size of the waves that form on the surface of a body of water; the longer the fetch and the stronger the wind, the more wind energy is imparted to the water surface and the larger the resulting {{gli|sea state}}.}}

{{defn|A scientific instrument used to measure the strength of electric fields in the atmosphere.}}

{{defn|A {{gli|whirlwind}} induced by a fire and often at least partially composed of flame or ash. They are usually associated with very large {{gli|wildfire|wildfires}}. Fire whirls are seldom classified as true {{gli|tornadoes}}, as their {{gli|vorticity}} usually derives from turbulent surface winds and heat-induced lifting rather than from a tornadic {{gli|mesocyclone}} aloft.}}

{{defn|A very large {{gli|wildfire}} or other conflagration which because of its intensity is able to create and sustain its own {{gli|Beaufort scale|storm-force}} winds. Firestorms develop when a convective {{gli|updraft}} of hot air rising from the burning area draws in strong wind {{gli|gusts}} from all directions, which supply the fire with additional oxygen and thereby induce further combustion. They are often associated with {{gli|flammagenitus}} clouds and {{gli|fire whirl|fire whirls}}.}}

{{defn|Any {{gli|flood}} which very rapidly inundates low-lying areas such as washes, rivers, dry lakes, and basins, especially one which recedes again in less than six hours. Flash flooding can be caused by heavy {{gli|rain}} associated with {{gli|severe weather}}, large amounts of meltwater from melting ice or snow, or the sudden collapse of a natural ice or debris dam.}}

{{defn|The process by which objects such as liquid {{gli|hydrometeor|hydrometeors}} are cooled below their freezing point very quickly, typically upon being subjected to extremely cold atmospheric temperatures or by making contact with a frozen surface.}}

{{defn|An overflow of water which submerges land that is usually dry. Flooding may occur when water bodies such as rivers, lakes, or oceans escape their boundaries by overtopping or puncturing levees, or it may occur when {{gli|precipitation}} accumulates on saturated ground more rapidly than it can either infiltrate or run off.}}

{{defn|A visible {{gli|aerosol}} of minute water droplets or ice crystals that is suspended in the air at or near the Earth's surface. Fog is often considered a type of low-lying {{gli|cloud}} and is heavily influenced by local topography, nearby bodies of water, and {{gli|wind}} conditions.}}

{{ghat|Also white rainbow, mist bow, and cloud bow.}}

{{defn|An optical phenomenon in which a whitish or faintly colored {{gli|primary rainbow}}, often with red and blue edges, is visible on a background of {{gli|fog}} or mist at the observer's {{gli|anti-solar point}}. It is caused by the refraction, reflection, and diffraction of light from the Sun or Moon by small water droplets with diameters less than {{convert|100|um|in|3}}.}}

{{defn|A type of warm, dry, downslope {{gli|wind}} that occurs in the {{gli|lee}} of a mountain range.}}

{{ghat|Often used interchangeably with {{gli|scud}}.}}

{{defn|A {{gli|cloud type}} or {{gli|cloud species|species}} consisting of ragged, irregularly shaped patches or shreds of {{gli|cumulus}} or {{gli|stratus}}.}}

{{defn|A type of {{gli|precipitation}} in which {{gli|drizzle}} consisting of supercooled liquid water droplets, often falling through a {{gli|temperature inversion}} in the lower atmosphere, freezes upon impact with the ground or other cold surfaces to form a coat of {{gli|glaze ice}}. Compare {{gli|freezing rain}}.}}

{{defn|A condition in which supercooled water droplets comprising {{gli|fog}} freeze either while suspended in the air, filling the air with visible {{gli|ice crystals}} similar to very light {{gli|snow}}, or upon contact with sub-freezing surfaces, forming a coating of {{gli|rime}} and/or {{gli|glaze ice}}.}}

{{defn|Liquid droplets of {{gli|rain}} that become supercooled while falling through a sub-freezing {{gli|air mass}} and then freeze upon impact with any surface they encounter; the resulting {{gli|glaze ice}} can accumulate to a thickness of several centimeters. Unlike {{gli|rain and snow mixed|mixed rain and snow}}, {{gli|ice pellets}}, and {{gli|hail}}, freezing rain exists entirely as a liquid until it hits a surface.}}

{{defn|no=1|A springtime thaw of snow and ice that produces a significant local inundation of rivers, streams, small watercourses, and floodplains as the snowpack melts within a watershed.}}

{{defn|no=2|Any temporarily inundated or rapidly flowing watercourse or newly created (and often ephemeral) drainage channel resulting from snowmelt.}}

{{defn|A boundary separating two {{gli|air mass|masses of air}} of different {{gli|atmospheric density|densities}} and usually also of different {{gli|temperature|temperatures}} and {{gli|humidity|humidities}}. Weather fronts are the principal cause of meteorological phenomena outside the {{gli|tropics}}, often bringing with them {{gli|clouds}}, {{gli|precipitation}}, and changes in {{gli|wind}} speed and direction as they move. Types of fronts include {{gli|cold fronts}}, {{gli|warm fronts}}, and {{gli|occluded fronts}}.}}

{{defn|The meteorological process by which a {{gli|front|weather front}} is created, usually as a result of the narrowing of one or more horizontal temperature gradients across the boundary between two adjacent {{gli|air masses}}. Contrast {{gli|frontolysis}}.}}

{{defn|The dissipation or weakening of an atmospheric {{gli|front|weather front}}. Contrast {{gli|frontogenesis}}.}}

{{defn|A very thin layer of {{gli|ice}} crystals on a solid surface, typically restricted to that which forms when {{gli|water vapor}} in an atmosphere whose temperature is above freezing comes into contact with a surface whose temperature is below freezing. Frost may exhibit a great variety of forms.}}

{{defn|A funnel-shaped {{gli|cloud}} associated with a rotating column of air and protruding from the {{gli|cloud base|base}} of a parent cloud but not reaching the ground or a water surface. Funnel clouds form most frequently in association with {{gli|supercell thunderstorms}} and often develop into {{gli|tornadoes}}.}}

G

{{defn|no=1|A strong surface {{gli|wind}}, typically used as a descriptor in nautical contexts and variously defined based on {{gli|wind speed|speed}}. In the modern {{gli|Beaufort scale}}, a gale is any {{gli|sustained wind}} of Beaufort number 7 or greater, corresponding to near gale at {{cvt|28|–|33|knot|kph mph|abbr=off}}; gale at {{cvt|34|–|40|knot|kph|abbr=off}}; strong gale at {{cvt|41|–|47|knot|kph|abbr=off}}; and storm at {{cvt|48|–|55|knot|kph|abbr=off}}.}}

{{defn|A local, low-level {{gli|wind}} that blows along a valley or through a col between mountains, often at speeds as high as {{convert|20|–|40|kn}}.}}

File:Earth Global Circulation - en.svg

{{defn|A measure of the vertical distance or altitude above mean sea level that accounts for variations in gravitational potential as altitude and latitude change. In meteorology and atmospheric science, geopotential height is often used in place of ordinary altitude when calculating the {{gli|primitive equations}} in {{gli|numerical weather prediction}} and when creating {{gli|atmospheric model|atmospheric models}}.}}

{{defn|The theoretical {{gli|wind}} that would result from an exact balance between the Coriolis force and the {{gli|pressure gradient}} force (known as geostrophic balance). The true wind almost always differs from the geostrophic wind due to the influence of other forces such as friction from the ground.}}

{{defn|A coating of smooth, clear {{gli|ice}}, sometimes of considerable thickness, that forms when supercooled water, usually precipitated as {{gli|freezing rain}} or {{gli|freezing drizzle}}, freezes upon contact with the ground or other exposed surfaces where the temperature (and that of the lower atmosphere) is at or below {{convert|0|C|F}}. Glaze is denser, harder, and more transparent than {{gli|rime}} and {{gli|hoarfrost}}.}}

{{defn|A type of observational meteorology that interprets the effects of atmospheric properties such as {{gli|precipitable water|total precipitable water vapor}} on the propagation of Global Positioning System (GPS) radio signals to derive information about the state of the local atmosphere.}}

{{defn|A type of {{gli|precipitation}} that forms when supercooled water droplets are collected and freeze on falling {{gli|snowflake|snowflakes}}, forming balls of {{gli|rime}} {{cvt|2|–|5|mm|in|abbr=on}} in diameter. Graupel is distinct from {{gli|hail}}, small hail, and {{gli|ice pellets}}.}}

{{defn|A {{gli|lake-effect snow}} that occurs in the lee of Utah's Great Salt Lake.}}

{{defn|An optical phenomenon consisting of a momentary glimmer of green light occasionally observed near the upper limb of the Sun's apparent disk just as it disappears from view at sunset or just as it appears at sunrise. It is most likely to be seen where there is a low, clear, distant horizon, such as over the ocean.}}

{{defn|A weather condition that occurs when loose snow or ice on the ground is lifted and blown into the air by strong winds. This can create low-visibility conditions even in the absence of precipitation.}}

{{defn|Information, such as local weather conditions, provided by direct observation (i.e. empirical evidence) as opposed to information provided by inference.}}

{{defn|A brief, sudden increase in the {{gli|wind speed|speed}} of the {{gli|wind}}, usually lasting less than 20 seconds. Gusts are more transient than {{gli|squall|squalls}} and are followed by a lull or slowing of the wind speed. They are generally only reported by {{gli|weather station|weather stations}} when the maximum wind speed exceeds the average wind speed by at least {{convert|10|–|15|kn|mph}}.}}

{{defn|See {{gli|outflow boundary}}.}}

{{defn|A relatively weak {{gli|tornado}} associated with the {{gli|outflow}} at the leading edge of a {{gli|storm cell|thunderstorm cell}}, and often occurring along a {{gli|outflow boundary|gust front}}. A {{gli|debris cloud}} or {{gli|dust whirl}} may indicate the presence of a gustnado.}}

H

{{defn|A type of solid {{gli|precipitation}} that consists of balls or irregular lumps of {{gli|ice}}, usually {{cvt|5|–|150|mm|in|abbr=on}} in diameter, each of which is called a hailstone. Hail formation requires environments with strong, upward motion of air and low altitudes at which water freezes, which makes it possible within most {{gli|thunderstorms}}. It is distinct from {{gli|graupel}} and {{gli|sleet}} or {{gli|ice pellets}}.}}

File:Hail storm 3.jpg

{{defn|Any {{gli|storm}}, usually a strong {{gli|thunderstorm}}, which precipitates {{gli|hail}}.}}

{{defn|A weather index that measures the potential for dry, unstable air to contribute to the development of large or erratic {{gli|wildfire|wildland fires}}. The index derives from data on the stability and {{gli|moisture|moisture content}} of the lower atmosphere and is calculated over three ranges of {{gli|atmospheric pressure}}.}}

{{defn|A type of {{gli|rime}} consisting of opaque, granular masses of ice deposited primarily on vertical surfaces by {{gli|freezing fog}}. Hard rime is more compact and amorphous than {{gli|soft rime}} and usually develops on windward surfaces exposed to high wind speeds and air temperatures between {{cvt|-2|and|-8|C|F}}.}}

{{defn|Any suspension in the atmosphere of very small, dry particulate matter, including natural {{gli|aerosols}} (e.g. dust, salt, or smoke) as well as man-made pollutants (e.g. {{gli|smog}}), the individual particles of which are invisible to the naked eye but collectively produce a milky, often opalescent sky with reduced {{gli|visibility}} at long distances. Haze usually indicates sub-saturated air, whereas {{gli|fog}} or mist indicates full saturation.}}

{{defn|The effect created by Earth's atmosphere trapping hot ocean air like a lid or cap.}}

{{defn|A rare phenomenon involving a sudden, localized increase in {{gli|surface temperature}} (sometimes {{convert|10|C-change|F-change}} or more within just a few minutes) associated with a decaying {{gli|thunderstorm}} or other {{gli|mesoscale convective system}} and possibly accompanied by {{gli|gust|gusty}} winds and a rapid decrease in {{gli|humidity}}.{{cite web |title=Glossary of Meteorology |url=http://amsglossary.allenpress.com/glossary/ |website=American Meteorological Society |archive-url=https://web.archive.org/web/20110606092844/http://amsglossary.allenpress.com/glossary/ |archive-date=June 6, 2011}}}}

{{ghat|Also apparent temperature, felt air temperature, and humiture.}}

{{defn|A meteorological index that posits the {{gli|apparent temperature}} perceived by the average human being who is exposed to a given combination of air {{gli|temperature}} and {{gli|relative humidity}} in a shaded area. For example, when the air temperature is {{cvt|32|C|F}} with 70% relative humidity, the heat index is {{cvt|41|C|F}}.}}

{{defn|A period of weather characterized by excessively high temperatures, which may or may not be accompanied by high {{gli|humidity}} or by {{gli|drought}}. Very hot weather is often only referred to as a heat wave if the temperature is abnormal relative to the typical climate for a given location during a given season. Contrast {{gli|cold wave}}.}}

{{defn|A type of weather warning formerly issued by the U.S. {{gli|National Weather Service}} to alert areas in which a high rate of {{gli|snow|snowfall}} (generally {{cvt|6|in|cm}} or more in 12 hours) was occurring or was {{gli|weather forecasting|forecast}}. The warning was replaced by the {{gli|Winter Storm Warning}} for Heavy Snow beginning with the 2008–09 winter storm season.}}

{{defn|A vectorial visual representation of the movement of a body or a fluid, with the position of any data plotted on it proportional to the velocity of the moving particle. In the context of meteorology, hodographs are used to plot {{gli|winds}} from {{gli|atmospheric sounding|atmospheric soundings}}: for a given vector, {{gli|wind direction}} is indicated by the angle from the center axis and {{gli|wind speed}} by the distance from the center.}}

{{defn|A measure of the amount of {{gli|water vapor}} present in a {{gli|air parcel|parcel}} of air. By quantifying the saturation of the air with moisture, humidity indicates the likelihood of {{gli|precipitation}}, {{gli|dew}}, or {{gli|fog}} occurring. The amount of water vapor needed to achieve full saturation increases as the air {{gli|temperature}} increases. Three primary measurements of humidity are widely employed in meteorology: {{gli|absolute humidity|absolute}}, {{gli|relative humidity|relative}}, and {{gli|specific humidity|specific}}.}}

{{defn|See {{gli|cumulus humilis}}.}}

{{defn|The local name for a {{gli|tropical cyclone}} that occurs in the Atlantic Ocean or northeastern Pacific Ocean and achieves one-minute maximum {{gli|sustained winds}} exceeding {{cvt|74|mph|kph kn}}.}}

{{defn|A {{gli|mudslide}} or {{gli|flash flood}} caused by torrential {{gli|rainfall}} occurring high in the Andes mountains of South America, especially during the weather phenomenon known as {{gli|El Niño}}.}}

{{defn|Any particulate of liquid or solid water within the {{gli|atmosphere}}, encompassing all types of {{gli|precipitation}}, formations due to condensation such as {{gli|clouds}} and {{gli|haze}}, and particles blown from the Earth's surface by wind such as {{gli|blowing snow}} and {{gli|sea spray}}.}}

{{defn|A branch of {{gli|meteorology}} and hydrology that studies the transfer of water and energy between land surfaces and the lower {{gli|atmosphere}}.}}

{{defn|The combined mass of all {{gli|ice|solid}}, liquid, and gaseous forms of water found on, beneath, or above the surface of the Earth, including all oceans, lakes, streams, groundwater, atmospheric {{gli|water vapor}}, snow, ice caps, and glaciers.}}

{{defn|A scientific instrument used to measure {{gli|humidity}}.}}

{{defn|The phenomenon by which a substance attracts and retains water molecules via either absorption or adsorption from the surrounding environment.}}

{{defn|A scientific instrument used to measure height or elevation, either by trigonometry or by the principle that {{gli|atmospheric pressure}} influences the boiling point of liquids.}}

I

{{defn|Water frozen into a solid state. Ice is abundant on Earth's surface and in the atmosphere and plays a major role in Earth's water cycle and {{gli|climate}}. Its natural occurrence in weather phenomena takes many forms, including {{gli|snowflakes}}, {{gli|hail}}, {{gli|frost}}, {{gli|icicles}}, and {{gli|ice spikes}}.}}

{{defn|no=1|A minute spicule of {{gli|ice}} that forms from water in the atmosphere at temperatures below the freezing point of {{convert|0|C|F}}. Ice crystals may take on any of a number of macroscopic, crystalline forms depending on the temperature at their formation, including needles, hexagonal prisms, and stars. Their growth occurs by the diffusion of {{gli|water vapor}} onto them, and they may collide with other ice crystals to form {{gli|snowflakes}}.}}

{{defn|no=2|A type of {{gli|precipitation}} composed of very small, unbranched crystals of ice which fall slowly and often seem to float in the air.}}

{{defn|A type of {{gli|fog}} consisting of a sufficient concentration of tiny {{gli|ice crystals}} suspended in the atmosphere to reduce {{gli|visibility}} to less than {{convert|1|km|mi}}. Ice fog forms at very low ambient air temperatures, typically {{convert|-30|C|F}} or below, usually in calm conditions at high latitudes but sometimes also as the result of mild maritime air blowing across ice- or snow-covered surfaces.}}

{{defn|A rare {{gli|ice}} formation that consists of a long, slender projection of ice extending upward from the surface of a frozen body of water, often in the shape of an inverted {{gli|icicle}}.}}

{{defn|A type of {{gli|winter storm}} characterized by {{gli|freezing rain}} which results in the accumulation of at least {{convert|6.4|mm|in}} of {{gli|ice}} on exposed surfaces.}}

{{defn|A long, slender spike of {{gli|ice}} formed when water dripping or falling from an object freezes.}}

File:Gdansk sople 2.jpg

{{defn|The influx of heat and moisture into a {{gli|storm}} system from the surrounding environment. The inflow of {{gli|air parcel|parcels}} of warm, moist air drives and sustains most types of storms, including {{gli|thunderstorms}} and {{gli|tropical cyclones}}. Contrast {{gli|outflow}}.}}

{{defn|A static {{gli|atmospheric model}} of the variations in {{gli|temperature}}, {{gli|atmospheric pressure|pressure}}, {{gli|atmospheric density|density}}, and viscosity over a wide range of altitudes within the Earth's atmosphere, established as an international standard by the International Organization for Standardization in order to provide a common reference for atmospheric variables relevant to meteorology and atmospheric science.}}

{{defn|See {{gli|cloud iridescence}}.}}

J

{{defn|See {{gli|canyon wind}}.}}

{{defn|A narrow, fast-flowing, meandering {{gli|air current}} primarily occurring in the upper part of the {{gli|troposphere}}, at altitudes above {{cvt|9|km|ft}}, and usually flowing from west to east. The Northern and Southern Hemispheres each have a predictable though discontinuous polar jet and subtropical jet; {{gli|low-level jet|low-level jets}} and other types of jet streams can form under certain conditions.}}

{{defn|The region of maximum {{gli|wind speed}} that runs along the elongated axis of a {{gli|jet stream}}. In the local winter, the maximum speed in the polar-front jet stream can reach upwards of {{convert|200|kn|kph mph}}.}}

K

{{defn|An operational atmospheric {{gli|stability index}} indicating the potential for {{gli|thunderstorms}}, based on temperature {{gli|lapse rate}}, {{gli|moisture content}} of the lower troposphere, and the vertical extent of the moist layer. K-index values of 36 and above suggest a high likelihood of thunderstorm development.}}

{{term| $K_{DP}$ }}

{{defn|A {{gli|warm front}} or {{gli|cold front}} that is overrun by drier air, or in which the warm air subsides, so that any clouds and precipitation tend to be suppressed, making them generally inactive fronts. Contrast {{gli|ana-front}}.}}

{{ghat|Also catabatic wind, drainage wind, or fall wind.}}

{{defn|A {{gli|local wind}} that carries cold, high-density air from a higher elevation downslope under the force of gravity as a result of the radiative cooling of the upland ground surface at night, usually at speeds on the order of {{cvt|10|knot|kph}} or less but occasionally at much higher speeds. Contrast {{gli|anabatic wind}}.}}

{{defn|A phenomenon of instability that occurs occasionally in an atmospheric layer within which {{gli|wind speed}} increases rapidly with {{gli|altitude}}. Kelvin–Helmholtz waves form in this layer of strong vertical {{gli|wind shear}}, and are often marked by a distinct train of clouds that resemble breaking ocean waves.}}

{{defn|The local name for a dry, hot, seasonal {{gli|wind}}, often carrying large quantities of {{gli|dust storm|dust or sand}}, that occurs in the deserts of Egypt, Israel, Palestine, and Jordan. Compare {{gli|haboob}}, {{gli|harmattan}}, {{gli|sirocco}}, and {{gli|simoom}}.}}

{{defn|A branch of classical mechanics that describes the motion of points, bodies, and systems of bodies without considering the forces that caused the motion.}}

{{defn|A unit of speed commonly used in maritime and aviation disciplines, equivalent to one nautical mile per hour ({{convert|1.1508|mph|m/s|disp=or}}). It is often used in meteorology for measuring {{gli|wind speed}}.}}

L

{{term| $L_{DR}$ }}

{{defn|A weather phenomenon produced when a cold {{gli|air mass}} moves across long expanses of warmer lake water, which causes the lowest layers of air to pick up warm {{gli|water vapor}} from the lake, rise through the upper layers, freeze and then precipitate on the lake's {{gli|leeward}} shores. In combination with {{gli|orographic lift}}, the effect produces narrow but very intense bands of {{gli|precipitation}}, especially {{gli|snow}}, which can deposit at very high rates and result in very large amounts of snowfall over a region. The same effect can also occur over bodies of salt water, when it is termed ocean-effect or bay-effect snow.}}

{{defn|A flow in which the particles of a fluid moves smoothly in parallel layers or sheets, i.e. without {{gli|turbulence}}.}}

{{defn|An offshore {{gli|local wind}} that blows from land to sea, usually at night, a result of the more rapid cooling of the land surface relative to the sea after sunset. It blows in the opposite direction of a {{gli|sea breeze}}, its daytime counterpart in a {{gli|diurnal}} cycle of coastal winds caused by lateral differences in surface temperature between land and sea.}}

{{defn|The movement of a {{gli|storm}} or other weather phenomenon over land after being over water.}}

{{defn|A type of {{gli|tornado}} emerging from a parent cloud that does not contain a pre-existing mid-level {{gli|mesocyclone}} or other rotation. Landspouts share a development process and resemblance with {{gli|waterspouts}}. They are generally smaller and weaker than {{gli|supercell}} tornadoes and are rarely detected by {{gli|Doppler weather radar}}.}}

{{defn|The rate at which an atmospheric variable, most commonly temperature or pressure, decreases with increasing {{gli|altitude}}.}}

{{defn|The amount of heat absorbed or released per unit mass during a change of phase of a substance at constant temperature and pressure. In meteorology, the term usually refers to the amount absorbed or released in the various transformations between the three physical states of water: ice, liquid water, and water vapor. For instance, the latent heat of vaporization requires about 2.4 million Joules per kilogram at 0 °C. Contrast {{gli|sensible heat}}.}}

{{defn|The movement of {{gli|water vapor}} (a major transporter of {{gli|latent heat}}) from one location to another, e.g. from the tropics toward the poles, where there is a persistent energy deficit relative to lower latitudes. Poleward latent heat flux reaches its global maximum of 1.5 × 10¹⁵ watts at latitudes 38 °N and 40 °S.}}

{{defn|A general statement of the manner in which the winds of a {{gli|cyclone}} rotate about the cyclone's center, and the way in which the entire {{gli|disturbance}} moves across the Earth's surface. The development by meteorologists of a "law" describing the general behavior of storms proved important in historical times to sailors navigating during storms at sea.}}

{{defn|See {{gli|stratiform}}.}}

{{ghat|Also lee depression, orographic depression, and dynamic trough.}}

{{defn|A {{gli|trough}} of {{gli|low-pressure area|low atmospheric pressure}} that forms preferentially to the {{gli|lee}} or downwind side of a mountain barrier when {{gli|air current|air currents}} flow in directions perpendicular to the barrier and become vertically "squashed" as they cross it. As the column resumes its original depth on the other side of the barrier, it tends to develop a strong spin about its vertical axis, which manifests as a low-pressure center.}}

{{defn|A method used by meteorologists which focuses on {{gli|updraft|updrafts}} and uses {{gli|Doppler weather radar|weather radar}} to determine the relative strength of {{gli|thunderstorm}} cells in a vertically {{gli|wind shear|sheared}} environment.}}

{{defn|The time interval during which a particular observation or observations in general have been maintained without interruption at a meteorological station, and which therefore serves as the frame of reference for climatic data at that station.}}

{{defn|A type of stationary {{gli|cloud}} with a distinct lens or saucer shape which typically forms in an arrangement perpendicular to the {{gli|wind direction}} and at altitudes less than {{convert|12|km|ft}} above sea level, most commonly above or near very large natural obstructions in the atmosphere, such as mountains and hills.}}

{{defn|The altitude in the atmosphere at which the temperature of the environment decreases faster than the {{gli|lapse rate|moist adiabatic lapse rate}} of a saturated {{gli|air parcel}} at the same level. Air masses with one or many LFCs are potentially unstable and may develop convective clouds such as {{gli|cumulonimbus}}.}}

{{defn|A surveying method that measures the distance to a target by illuminating the target with pulsed laser light and measuring the reflected pulses with a sensor; differences in laser return times and wavelengths can then be used to create digital three-dimensional representations of the target. The name is now used as an acronym of light detection and ranging.}}

{{defn|The difference in temperature between the ambient environment and an {{gli|air parcel}} that is lifted {{gli|adiabatic process|adiabatically}} at a given {{gli|atmospheric pressure|pressure}} height within the {{gli|troposphere}}, typically {{convert|500|hPa|atm}}. When the value of the lifted index is positive, the atmosphere at the given height is stable; when it is negative, the atmosphere is {{gli|convective instability|unstable}}.}}

{{defn|A naturally occurring electrostatic discharge during which two electrically charged regions of the atmosphere or ground temporarily equalize themselves, instantaneously releasing about a billion joules of energy across a wide range of the electromagnetic spectrum, from very hot plasma to brilliant flashes of light visible in the atmosphere. Lightning is often followed by its audible consequence, {{gli|thunder}}, and is one of the distinguishing features of {{gli|thunderstorms}}. Lightning phenomena are generally separated into three classes based on where they occur – either inside a single cloud, between two different clouds, or between a cloud and the ground – but many other observational variants have been recognized.}}

{{defn|Any {{gli|lightning}} discharge that occurs between the atmosphere and an object (rather than between different parts of the atmosphere). Most lightning strikes are {{gli|cloud-to-ground lightning|cloud-to-ground}}, meaning they terminate on the Earth's surface or on an object attached to it, but lightning can also strike airborne objects or travel from {{gli|ground-to-cloud lightning|ground-to-cloud}}. The primary electron-conducting channel in such discharges, visible for a fraction of a second as a very bright, "zigzagging" path of light, is sometimes called a lightning bolt.}}

File:Leaderlightnig.gif

File:Lithometeor.Sonnenuntergang.Saharastaub.P1024931.jpg

{{defn|An instrument used to measure the total amount of evapotranspiration that occurs within a certain area of the Earth's surface, usually by recording the amount of precipitation received by the area and the amount of moisture subsequently lost through the soil.}}

M

{{defn|A sky that is partially or fully {{gli|cloud cover|covered}} by high {{gli|altocumulus}} or {{gli|cirrocumulus}} clouds with a regular pattern of ripples and patches separated by small areas of blue sky, resembling the scales on a mackerel.}}

{{defn|A strong {{gli|downburst}} that affects a path longer than {{convert|4|km|mi}} and persists for up to 30 minutes, with surface winds reaching as high as {{convert|210|kph|mph}}.}}

{{defn|The study of the largest-scale {{gli|meteorology|meteorological}} processes, i.e. those occurring over very large regions, oceans, continents, or the entire Earth, such as the {{gli|general circulation}}, as opposed to {{gli|mesoscale meteorology|mesometeorology}} and {{gli|microscale meteorology|micrometeorology}}. See also {{gli|synoptic-scale meteorology}}.}}

{{defn|A North American system used in the transmission of marine {{gli|weather forecasting|weather forecasts}} to compress large amounts of information about meteorological and marine conditions, including visibility, expected future wind speed and direction, the "state of sea", and the period of validity of the forecast, into shorter code for convenience during radio broadcasting. MAFOR is an abbreviation of MArine FORecast.}}

{{defn|A scientific instrument consisting of a liquid column gauge used to measure differences in the pressures of gases, as with a {{gli|barometer|mercury barometer}}.}}

{{defn|A regional {{gli|climate}} that is strongly influenced by its location in relation to a sea or ocean, characterized by relatively small {{gli|diurnal variation|diurnal}} and {{gli|season|seasonal}} temperature variations and high atmospheric {{gli|moisture content}}, which contributes to high {{gli|precipitation}} and {{gli|humidity}}. Contrast {{gli|continental climate}}.}}

{{defn|The movement of a fluid, such as an {{gli|air mass}}, down a {{gli|pressure gradient|pressure}} or {{gli|temperature gradient}}.}}

{{defn|The component of the large-scale atmospheric {{gli|general circulation}} that is oriented parallel to a meridian or line of longitude, and thus shows large north–south movement.}}

{{defn|The third major layer of the Earth's {{gli|atmosphere}}, above the {{gli|stratosphere}} and below the {{gli|thermosphere}}. The lower boundary of the mesosphere varies between {{cvt|50|and|65|km|mi}} above the Earth's surface, depending on latitude and time of year.}}

{{defn|A branch of the {{gli|atmospheric science|atmospheric sciences}} which seeks to understand and explain observable {{gli|weather}} events, with a major focus on {{gli|weather forecasting|weather prediction}}. Meteorology uses variables familiar in chemistry and physics to describe and quantify meteorological phenomena, including {{gli|temperature}}, {{gli|atmospheric pressure|pressure}}, {{gli|water vapor}}, {{gli|mass flow}}, and how these properties interact and change over time.}}

{{defn|A weather observation network even denser than a {{gli|mesonet}}, such as the Oklahoma City Micronet.}}

{{defn| Meteorological phenomena that occur on a scale of 40 m to 4 km.{{cite web|url=https://glossary.ametsoc.org/wiki/Misoscale |title=Misoscale - Glossary of Meteorology |publisher=Glossary.ametsoc.org |date=2012-01-26 |accessdate=2022-08-12}}}}

{{defn|A distinct kind of {{gli|supercell}} that is smaller than a typical supercell.}}

{{defn|A fallacious term often used in news media to refer to damaging winds accompanying a {{gli|thunderstorm}}, indifferently caused by {{gli|tornadoes}} or {{gli|microbursts}}, on a small area.}}

{{defn|A vortex with a width between {{convert|40|m|ft}} and {{convert|4|km|mi}},{{cite web|url=https://glossary.ametsoc.org/wiki/Misocyclone |title=Misocyclone - Glossary of Meteorology |publisher=Glossary.ametsoc.org |date=2015-04-14 |accessdate=2022-08-12}} which in the strictest sense includes {{gli|waterspouts}} and {{gli|landspouts}}.}}

{{defn|A {{gli|cloud}} composed of both liquid water droplets and {{gli|ice crystal|ice crystals}} (e.g. {{gli|altostratus}}, {{gli|cumulonimbus}}, and {{gli|nimbostratus}}), as opposed to a {{gli|warm cloud}}.}}

{{defn|A measure of atmospheric {{gli|moisture content}}, usually expressed as the dimensionless ratio of the mass of water vapor in a given {{gli|air parcel|parcel of air}} to the unit mass of dry air (i.e. grams of water vapor per kilogram of dry air).}}

{{defn|See {{gli|parhelion}}.}}

{{defn|An update to the original {{gli|Fujita scale}} from 1971 proposed by Ted Fujita in 1992.}}

{{defn|See {{gli|saturated adiabat}}.}}

{{defn|See {{gli|saturated adiabatic lapse rate}}.}}

{{defn|An area where moisture concentrates due to the air flow near the surface.}}

{{defn|See {{gli|gap wind}}.}}

{{defn|A {{gli|thunderstorm}} consisting of more than one {{gli|convection cell}}, i.e. more than one circulating system of {{gli|updraft|updrafts}} and {{gli|downdraft|downdrafts}}.}}

{{defn|The presence of liquid, especially water, within a body or substance, often in trace amounts. Moisture in the air in the form of {{gli|water vapor}} underlies the concept of {{gli|humidity}}.}}

{{defn|no=1|An abrupt seasonal {{gli|wind}} reversal accompanied by corresponding changes in {{gli|precipitation}}.}}

{{defn|no=2|Any seasonal change in {{gli|atmospheric circulation}} and precipitation associated with the asymmetric heating of land and sea. In this context, the term is often used to refer specifically to the {{gli|wet season|rainy phase}} of such a pattern, and in some places colloquially (and less correctly) to any locally very heavy but short-term rainfall.}}

{{defn|See {{gli|wall cloud}}.}}

N

{{defn|A rare type of {{gli|polar stratospheric cloud}} that forms at altitudes of {{convert|24|–|30|km|ft}}, usually in high-latitude regions. These clouds are normally {{gli|lenticular}} in form but may resemble {{gli|cirrus}}, and often exhibit brilliant {{gli|cloud iridescence|iridescence}} similar to mother-of-pearl shortly after sunset or before sunrise.}}

{{defn|A predecessor forecasting center to the {{gli|Storm Prediction Center}} that was located in Kansas City, Missouri.}}

{{defn|A {{gli|National Oceanic and Atmospheric Administration|NOAA}} lab in Norman, Oklahoma tasked with researching {{gli|severe weather}}.}}

{{defn|The official NOAA record of all known {{gli|tornadoes}} within the United States from 1950 to present.}}

{{defn|The national meteorological agency of the United States, tasked with providing {{gli|weather forecasting|weather forecasts}}, warnings of {{gli|severe weather}}, and other weather-related services to organizations and the public for the purposes of protection, safety, and general information.}}

{{defn|A small-amplitude oceanic {{gli|tide}} of minimum tidal range occurring semi-monthly near the times when the Moon is in quadrature, i.e. the first and third quarters.}}

{{defn|The angular displacement of a {{gli|trough}} line such that the axis of the trough is rotated clockwise from a north–south meridian (as opposed to the counterclockwise rotation of a {{gli|positive tilt|positively tilted}} trough); in the Northern Hemisphere, negative tilt corresponds to a northwest-to-southeast orientation. Most troughs begin with a positive tilt and gradually become neutral (north–south) and then negatively tilted as the flow of cold air distorts their shape. Positive tilt thus indicates the building phase of the trough, when clouds and precipitation develop, and negative tilt indicates the dissipation of its energy, when the most severe weather occurs.}}

{{defn|The scientific study of {{gli|clouds}}.}}

{{defn|A scientific instrument used to measure the altitude, direction, and velocity of atmospheric {{gli|clouds}} relative to a point on the ground directly below them.}}

{{defn|A {{gli|cloud type|genus}} of {{gli|cloud}} occurring at low or middle altitudes, typically between {{convert|0.5|and|5.5|km|ft}}, and often appearing as a dull, dark gray, ragged, nearly uniform sheet or layer that obscures the Sun and produces more or less continuously falling light to moderate {{gli|precipitation}} but no lightning or thunder. Low, ragged {{gli|fractus}} clouds frequently occur below nimbostratus and may or may not merge with it.}}

{{defn|See {{gli|diabatic process}}.}}

{{defn|A macro-scale {{gli|extratropical cyclone}}, especially one which impacts the middle and north Atlantic coasts of North America. The name derives from the direction of the winds that most strongly affect the eastern seaboard between the months of October and March. Such storms are often accompanied by very heavy rain or snow, which can cause severe coastal flooding, and {{gli|Beaufort scale|hurricane-force}} winds.}}

{{ghat|Also Canterbury arch; associated with nor'wester.}}

{{defn|A conspicuous high-altitude arch-shaped cloud formation that appears regularly in otherwise clear blue skies above the east coast of New Zealand's South Island, when a strong, hot, northwesterly {{gli|föhn wind}} (known as "The Nor'wester") pushes cooling moist air over the Southern Alps.}}

{{defn|The average value of a meteorological element (e.g. temperature, precipitation, humidity) over a given {{gli|period of record|period of time}}, most commonly three consecutive 10-year intervals totaling 30 years.}}

{{defn|See {{gli|aurora}}.}}

O

{{defn|Any atmospheric phenomenon exclusive of clouds that restricts {{gli|vertical visibility}}, including various {{gli|hydrometeor|hydrometeors}} such as {{gli|rain}} and {{gli|snow}} as well as {{gli|lithometeor|lithometeors}} such as dust and sand.}}

{{defn|A type of {{gli|front}} formed during the process of {{gli|cyclogenesis}} when a {{gli|cold front}} overtakes a {{gli|warm front}}. Occluded fronts usually form around mature {{gli|low-pressure area|low-pressure areas}} when a warm {{gli|air mass}} is physically separated (or "occluded") from the cyclonic center at the Earth's surface by the intervention of a cooler air mass; the warmer air is lifted into a {{gli|trowal|trough of warm air aloft}}. In {{gli|surface weather analysis}}, occluded fronts are symbolized by various combinations of the symbols for cold and warm fronts.}}

{{defn|Any regular, permanent or semi-permanent movement or flow of ocean water, either in a cyclic pattern or as a continuous stream along a defined path. Ocean currents are generally driven by {{gli|wind}} or by {{gli|geostrophic}} forces related to seawater density gradients. They are major transporters of the heat introduced by solar radiation, usually moving warm water from the {{gli|tropics}} to higher latitudes and returning cold water in the opposite direction, by which they exert an important influence on {{gli|climate}} and weather phenomena across the world.}}

{{defn|See {{gli|marine climate}}.}}

{{defn|Any {{gli|ocean current}} that flows parallel to, or away from, the coastline of a landmass.}}

{{defn|Any {{gli|wind}} that blows from land out over a body of water, e.g. a {{gli|land breeze}}. Contrast {{gli|onshore wind}}.}}

{{defn|A unit of measurement used to describe the amount of {{gli|cloud cover}} at a given location in terms of how many eighths of the {{gli|sky}} are covered in clouds, ranging from 0 oktas (completely clear) to 8 (completely {{gli|overcast}}) or sometimes 9 oktas (indicating that the sky is obstructed from view).}}

{{defn|Any {{gli|wind}} that blows from a body of water to land, e.g. a {{gli|lake breeze|lake}} or {{gli|sea breeze}}. Contrast {{gli|offshore wind}}.}}

{{defn|Any {{gli|cloud}} whose form and extent is determined by the effects of high-elevation terrain upon the passing flow of air, especially the forced {{gli|orographic lift|uplift}} of moist air as it passes over hills or mountains. As the rising air mass encounters reduced atmospheric pressures, {{gli|adiabatic cooling}} commonly results in condensation and {{gli|precipitation}}. Orographic clouds are usually very slow-moving or stationary; examples include {{gli|lenticular cloud|lenticular clouds}} and {{gli|cap cloud|cap clouds}}.}}

{{defn|The forced ascent of an {{gli|air mass}} as it passes over a topographic barrier such as a range of hills or mountains. If the air is moist, the uplift may result in {{gli|adiabatic cooling}}, leading to saturation, condensation, and the formation of {{gli|orographic cloud|orographic clouds}} and often {{gli|precipitation}}.}}

{{defn|The condition of {{gli|cloud clover}} wherein {{gli|clouds}} obscure at least 95% of the sky. The type of cloud cover that qualifies as overcast is distinguished from obscuring surface-level phenomena such as {{gli|fog}}.}}

{{defn|The action of an {{gli|air mass}} aloft, often relatively warm, moving over another air mass of greater density at the surface, as occurs in a {{gli|warm front}}.}}

{{defn|A distinct, bulging protuberance produced by a vigorous {{gli|updraft}} that rises above the top of the {{gli|anvil}} of a {{gli|cumulonimbus}} cloud. Overshooting tops are generally short-lived, but those that persist may indicate the potential for strong {{gli|thunderstorms}} and {{gli|severe weather}}.}}

{{defn|Air that flows outwards (away from) a {{gli|storm}} system. Outflow typically radiates from {{gli|thunderstorms}} in the form of a wedge of rain-cooled air, which is often delineated by a low, thick cloud preceded by a {{gli|outflow boundary|gust front}}, apparent both from the ground and in {{gli|weather radar}} imagery. The altitude at which the outflow occurs is strongly correlated with the intensity and persistence of large storm systems such as {{gli|tropical cyclones}}.}}

{{defn|The boundary between the cooled {{gli|outflow}} air from a {{gli|thunderstorm}} and the air of the surrounding environment, similar to a {{gli|cold front}}. New thunderstorms often develop along outflow boundaries.}}

{{defn|A region of the Earth's {{gli|atmosphere}} containing relatively high concentrations of the gaseous chemical ozone (O₃) and which is responsible for absorbing more than 97 percent of the Sun's incoming medium-frequency ultraviolet (UV) radiation. The ozone layer is found mainly in the lower portion of the {{gli|stratosphere}}, between approximately {{convert|15|and|35|km|mi}} in altitude, although its thickness varies seasonally and geographically.}}

P

{{defn|A form of {{gli|ice}} that consists of round, flat pieces of ice with elevated rims, with diameters ranging from {{cvt|30|cm|in}} to {{cvt|3|m|ft}}, and thicknesses of up to {{cvt|10|cm|in}}.}}

{{ghat|Also scud; often used interchangeably with {{gli|fractus cloud|fractus}}.}}

{{defn|An optical phenomenon in which a patch of bright light is visible along the main 22° {{gli|halo}} around the Sun, commonly occurring as a pair of such patches with one on either side of the solar disk; the halo itself is not always visible. More rarely, parhelia may occur at other points on the parhelic circle. They are caused by the refraction of sunlight by airborne {{gli|ice crystals}} with diameters less than {{cvt|30|um|in}}, e.g. those present in {{gli|cirrus}} or {{gli|cirrostratus}} clouds.}}

{{defn|The SI derived unit of pressure, defined as one newton per square metre. In meteorology, measurements of {{gli|atmospheric pressure}} are often given in hectopascals (hPa) or kilopascals (kPa).}}

{{defn|A hydrostatic principle which states that pressure applied to a confined incompressible fluid (e.g. {{gli|air}}) is transmitted equally and undiminished to every portion of the fluid and to the walls of the containing vessel.}}

{{defn|A {{gli|tornado}} rating scale developed by Allen Pearson differentiating path length (P) and path width (P) to accompany NOAA {{gli|Fujita scale}} (F) ratings.}}

{{defn|See {{gli|wall cloud}}.}}

{{defn|A period of five consecutive days sometimes used in preference to the seven-day week in the analysis of meteorological data because it divides conveniently into the number of days (365) in a standard year.}}

{{defn|The length of time during which a specific meteorological element (e.g. temperature, humidity, precipitation, etc.) has been officially observed and recorded at a particular place.}}

{{defn|A {{gli|cloud variety}} characterized by a widespread sheet or patch of cloud with distinct gaps between the cloud elements such that the Sun, Moon, clear sky, or overlying clouds are visible from the ground. It is most often applied to {{gli|stratocumulus}} and {{gli|altocumulus}}.}}

{{defn|Any bright object or other optical phenomenon appearing in the Earth's atmosphere when sunlight or moonlight creates a reflection, refraction, diffraction, or interference under particular circumstances. Common examples of photometeors include {{gli|halos}}, {{gli|coronae}}, {{gli|rainbows}}, {{gli|crepuscular rays}}, and {{gli|sun dogs}}.}}

{{defn|A branch of {{gli|meteorology}} concerned with the structure and composition of the {{gli|atmosphere}} and the various optical, electrical, acoustical, and thermodynamic phenomena that characterize it, including {{gli|aerosol|aerosols}} and {{gli|clouds}}, {{gli|precipitation}}, and electromagnetic radiation.}}

{{term|Phi_DP ( $\Phi_{DP}$ )}}

{{defn|A small {{gli|accessory cloud}}, appearing as a smooth, shallow, {{gli|lenticular cloud|lenticular}} "cap", that forms above or attached to the top of a {{gli|cumulus}} or {{gli|cumulonimbus}} cloud. Pileus clouds are formed when moist air above the parent cloud is cooled to its {{gli|dew point}} by a strong {{gli|updraft}}, and are good predictors of {{gli|thunderstorms}}; a pileus atop a cumulus cloud often foreshadows its transformation into a cumulonimbus cloud.{{Cite book|title=An Introduction to Clouds : From the Microscale to Climate|last=Ulrike|first=Lohmann|author-link=Ulrike Lohmann|others=Lüönd, Felix,, Mahrt, Fabian|isbn=9781139087513|location=Cambridge|page=288|oclc=953455396}}}}

{{defn|See {{gli|ceiling balloon}}.}}

{{defn|An inflight report by an aircraft pilot or crew member of the {{gli|weather}} experienced by the aircraft. A complete coded report typically includes information about the location and/or extent of reported weather phenomena; the time of observation; a description of the phenomena; the altitude of the phenomena; and the type or status of the aircraft.}}

{{defn|An extensive {{gli|high-pressure area}} across the polar latitudes of either the Northern or Southern Hemisphere which acts as a source of very cold and generally dry air. The {{gli|anticyclone}} over the Arctic, known as the Arctic high, is generally seasonal, while that over Antarctica, known as the Antarctic high, is semi-permanent.}}

{{defn|A relatively small-scale, non-frontal, migratory {{gli|low-pressure area|low-pressure}} {{gli|pressure system|system}} that occurs in the polar latitudes of either the Northern or Southern Hemisphere. Such systems are {{gli|secondary depression|secondary depressions}} that form over oceans poleward of the {{gli|polar front}}, most commonly during the local {{gli|winter}}, and can produce blustery, snowy conditions.}}

{{defn|Either of the two semi-permanent, semi-continuous {{gli|front|boundaries}} separating warm, moist tropical air from cold, dry polar air in the middle latitudes of the Northern and Southern Hemispheres. The northern polar front can often be traced as a continuous line of several thousand kilometers over the North Atlantic and North Pacific Oceans. It is the most significant front in terms of air mass contrast and susceptibility to {{gli|cyclonic}} disturbance.}}

{{defn|Either of the two very large, persistent, rotating, upper-level {{gli|low-pressure area|low-pressure areas}} suspended in the Earth's atmosphere near the geographic poles. The polar vortices predictably strengthen during their local winter and weaken during their local summer as the temperature contrast between the poles and the Equator changes. When either vortex is weak, high-pressure zones of lower latitudes may push poleward, driving the vortex, {{gli|jet stream}}, and masses of cold, dry polar air into the mid-latitudes, which can cause sudden, dramatic drops in temperature known as {{gli|cold wave|cold waves}}.}}

{{defn|A sudden bright light caused when an overhead power line is severed or especially when a transformer explodes. {{gli|Severe weather}} is one of the most common causes.}}

{{defn|The depth of water, in millimeters or inches, that could be measured if all of the water in a column of the atmosphere were {{gli|precipitation|precipitated}} as {{gli|rain}}.}}

{{defn|Any product of the condensation of atmospheric {{gli|water vapor}} that falls by gravity, the main forms of which include {{gli|rain}}, {{gli|sleet}}, {{gli|snow}}, {{gli|hail}}, and {{gli|graupel}}. Precipitation occurs when a portion of the atmosphere becomes locally saturated with water vapor such that the water condenses into liquid or solid droplets and thus "precipitates" out of the atmosphere.}}

{{defn|The horizontal or vertical rate of change of {{gli|barometer|barometric}} {{gli|atmospheric pressure|pressure}} in the {{gli|atmosphere}}, usually expressed in {{gli|pascal|hectopascals}} (hPa) per metre; the term is also sometimes used more loosely to denote simply the magnitude of the gradient within a pressure field. The three-dimensional pressure gradient vector is usually resolved into its vertical and horizontal components.}}

{{defn|The force experienced by a unit mass of {{gli|air mass|air}} in response to differences in {{gli|atmospheric pressure}} in either the horizontal or vertical plane, i.e. a {{gli|pressure gradient}}, such that {{gli|air parcel|air parcels}} are accelerated away from regions of high pressure and toward regions of low pressure. A strong pressure gradient force leads to intense atmospheric flows and strong {{gli|winds}}.}}

{{defn|A relative peak or lull in the spatial distribution of sea-level {{gli|atmospheric pressure}}. {{gli|high-pressure area|High-}} and {{gli|low-pressure area|low-pressure}} systems evolve by the interactions of {{gli|temperature}}, {{gli|moisture}}, and {{gli|solar irradiance|solar radiation}} in the atmosphere, and are directly responsible for most local {{gli|weather}} phenomena.}}

{{defn|The predominant {{gli|winds}} encountered at a particular point or region of the Earth's surface, identified by their source and {{gli|wind direction|direction}}. Though wind speed and direction can vary widely for a given location at a given time, the prevailing winds represent the primary trend in the characteristics of local winds averaged over a long period of time. They are influenced both by global patterns of atmospheric {{gli|air current|air movements}} and by local topography.}}

{{defn|The field of engineering concerned with the physical and thermodynamic properties of gas-vapor mixtures, especially the mixture of air and {{gli|water vapor}}.}}

{{defn|A {{gli|thunderstorm}} that produces brief but strong {{gli|updraft|updrafts}}, common in humid areas of the continental United States during the {{gli|summer}}. These storms are often associated with {{gli|severe weather}}, particularly sudden and intense wind {{gli|gusts}}, very large {{gli|hail|hailstones}} which grow continuously as they are repeatedly moved up and down within the storm, and {{gli|flash flooding}}.}}

{{defn|A type of {{gli|actinometer}} used to measure {{gli|solar irradiance}} on a planar surface and solar flux density in the hemisphere above.}}

Q

{{defn|In {{gli|quasi-geostrophic theory|quasi-geostrophic}} and semi-geostrophic theory, a horizontal vector which appears in the {{gli|omega equation}} and tends to point in the direction of rising air. If $Q$ points toward warm air, the {{gli|geostrophic flow}} is {{gli|frontogenesis|frontogenetic}}; if it points toward cold air, the geostrophic flow is {{gli|frontolysis|frontolytic}}.}}

{{defn|A method of estimating the approximate amount or rate of {{gli|precipitation}} that has fallen at a location or across a region based on radar measurements or satellite data.}}

{{defn|A prediction of the amount of {{gli|precipitation}} that will fall at a given location within a given time period, expressed in units of depth (e.g. inches).}}

{{defn|A marked oscillation in the {{gli|zonal}} {{gli|winds}} in the lower part of the equatorial {{gli|stratosphere}}, in which the {{gli|wind direction|direction}} changes gradually from westerly to easterly and back to westerly with a period that fluctuates between approximately 24 and 30 months.}}

{{ghat|Also geostrophic approximation and pseudogeostrophic approximation.}}

{{defn|A form of the {{gli|primitive equations|primitive}} equations of motion in which the {{gli|geostrophic wind}}, an idealized approximation to the actual {{gli|wind}}, is used to simplify the system of momentum and thermodynamic equations known as the quasi-geostrophic equations. These equations are derived from an expansion of terms in powers of the {{gli|Rossby number}}, which is presumed small. The quasi-geostrophic approximation is useful in the analysis of {{gli|extratropical cyclone|extratropical}} {{gli|synoptic meteorology|synoptic-scale}} systems, but less accurate in situations in which the {{gli|ageostrophic wind}} plays an important {{gli|advection|advective}} role, e.g. near {{gli|fronts}}.}}

{{defn|The flow of a fluid in which an approximate {{gli|geostrophic balance}} between the Coriolis force and the {{gli|pressure gradient force}} holds, but for which other terms such as the inertial terms involving temporal change or advective acceleration still play a key dynamic role despite their relatively small magnitude.}}

{{defn|A theory of atmospheric dynamics that involves the {{gli|quasi-geostrophic approximation}} in the derivation of the quasi-geostrophic equations. This theory is relatively accurate for {{gli|synoptic meteorology|synoptic-scale}} atmospheric motions in which the {{gli|Rossby number}} is less than unity, but it cannot accurately describe some local atmospheric structures such as {{gli|fronts}} or small, strong {{gli|low-pressure area|low-pressure}} cells as well as other theories.}}

{{defn|See {{gli|squall line}}.}}

{{defn|A {{gli|front}} that is {{gli|stationary front|stationary}} or nearly so; conventionally, a front that is moving at a speed less than about {{convert|5|knots|mph}}.}}

R

{{defn|The portion of the pulsed beam of microwave energy emitted by a radar transmitter that is reflected back to the receiver after the signal encounters a specific target or obstruction in the atmosphere, such as individual particles of {{gli|precipitation}}. The term may also refer to the {{gli|backscatter}} produced by these objects.}}

{{defn|Any method that uses radar technology to map the location and characteristics of selected environmental phenomena by emitting a pulse of microwave radiation at a target and analyzing the portion that is partially {{gli|radar echo|returned}} by {{gli|backscattering}}. Radar imaging is widely used in the atmospheric sciences to create images indicating large-scale spatial patterns of meteorological data, e.g. the intensity and distribution of {{gli|precipitation}}, or the height and orientation of wind-driven ocean waves.}}

{{defn|A branch of {{gli|meteorology}} concerned with the use of primarily ground-based radar technologies for the analysis and {{gli|weather forecasting|prediction}} of atmospheric phenomena across a wide variety of spatial scales.}}

{{defn|Atmospheric motion detected by using radar to track a target attached to a {{gli|radiosonde}}, or by {{gli|Doppler radar}}.}}

{{defn|{{gli|fog|Fog}} formed over land, generally at night in moist, calm air under clear skies. The most common type of fog, it is caused by the radiative cooling of the Earth's surface and the lowest layers of the atmosphere when the temperature of the air near the ground decreases below its {{gli|dew point}}. Radiation fog occurs most often in the autumn and winter, and is often deepest around sunrise but usually disperses after dawn when heated by solar radiation.}}

{{defn|A battery-powered scientific instrument released into the {{gli|atmosphere}}, usually by a {{gli|weather balloon}}, which measures various {{gli|atmospheric sounding|atmospheric variables}} and transmits them by radio telemetry to a ground receiver. Radiosondes are essential sources of meteorological data.}}

{{defn|The distance between the center of a {{gli|cyclone}} and its band of strongest {{gli|winds}}, often used as a metric for determining a cyclone's potential intensity.}}

{{defn|A type of {{gli|precipitation}} that occurs when liquid water in the form of droplets condenses from atmospheric {{gli|water vapor}}, becoming heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth.}}

{{defn|A {{gli|cloud}} and {{gli|precipitation}} structure associated with an elongated area of {{gli|rainfall}} and generated by differences in temperature. Rainbands may develop as {{gli|squall lines}} ahead of {{gli|cold fronts}}; {{gli|tropical cyclones}} are usually composed of multiple curved rainbands.}}

{{defn|An optical phenomenon that takes the form of a circular arc of light separated into concentric colored bands consisting of all of the individual colors of the visible spectrum, which occurs when sunlight is refracted as it passes through water droplets in the atmosphere and is then reflected from the rear of the droplets. In a primary bow, usually appearing with an angular distance of 42° centered on the {{gli|anti-solar point}}, the color separation produces a spectrum with red on the outer edge of the arc and violet on the inner edge; a secondary bow, with an angular distance of 51°, is also sometimes visible, but the colors are typically much dimmer and appear in the reverse order.}}

{{defn|An annually recurring period of one or more months during which {{gli|precipitation}}, particularly {{gli|rainfall}}, is at or near its average annual maximum for a certain region. The term is used especially in {{gli|tropics|tropical}} climates, where the rainy season contrasts with the {{gli|dry season}}.}}

{{defn|A class of {{gli|precipitation}} composed of both {{gli|rain}} and {{gli|snow}}, the latter usually partially melted, that is reported in some weather observation formats. It usually occurs only briefly at any one location as a transition phase from rain to snow or vice versa.}}

{{defn|An instrument used to collect and measure the amount of liquid {{gli|precipitation}} that occurs within a certain area over a certain period of time.}}

{{defn|A relatively and consistently dry area on the {{gli|leeward}} side of a significant geographic uplift such as a mountain range. Rain shadows exist because the uplift acts as a barrier to the passage of {{gli|precipitation}}-producing weather systems: moist air masses crossing high elevations are forced upward by {{gli|orographic lift}}, which causes the moisture to condense and precipitate on the {{gli|windward}} side, leaving the air depleted of moisture by the time it reaches the leeward side.}}

{{ghat|Often simply {{gli|showers}}.}}

{{defn|Short, intense periods of {{gli|rainfall}}, especially when occurring in widely scattered locations.}}

{{defn|A {{gli|local wind}} generated as a result of a {{gli|pressure gradient}} between two ends of a narrow valley, blowing from higher to lower pressure (usually in the downstream direction), with its velocity increased by the funneling effect of the ravine itself.}}

{{defn|A type of {{gli|weather balloon|balloon}}-borne {{gli|radiosonde}} that is tracked using position change as determined by radar or {{gli|theodolite|radiotheodolite}} in order to specifically measure {{gli|wind speed}} and {{gli|wind direction|direction}} aloft, and sometimes also other meteorological variables.}}

{{defn|A {{gli|weather forecast}} for a specified geographic region, usually a wider area than that covered by a {{gli|local forecast}}.}}

{{defn|The acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to on-site observation. In meteorology, satellite- or aircraft-based sensor technologies are widely used to detect and classify objects on the surface or within the atmosphere or oceans based on propagated electromagnetic signals.}}

{{defn|no=1|A strong northwesterly {{gli|wind}} that blows across the Caucasus Mountains from the Black Sea in the west to the Caspian Sea in the east.}}

{{defn|no=2|A {{gli|local wind}}, cold in winter and hot in summer, that affects northern Syria, northern Iraq, western Iran, and southeastern Turkey.}}

{{defn|Any motion of an atmospheric wave or {{gli|pressure system}} that opposes, or occurs in a direction opposite to, the normal or typical flow in which it is embedded, e.g. a situation in which {{gli|Rossby wave|Rossby waves}} move westward, contrary to the generally westerly winds flowing through the pattern.}}

{{term|Rho_hv ( $\rho_{hv}$ )}}

{{defn|An elongated region of relatively {{gli|high-pressure area|high atmospheric pressure}}, almost always associated with an area of maximum {{gli|anticyclonic}} curvature of wind flow. Ridges may exist at the surface or aloft or both; they may contain the closed circulation of a distinct high-pressure area, and a high may have one or more distinct ridges. Under certain conditions, ridges may alternate with {{gli|troughs}} in a high-amplitude pattern.}}

{{defn|A coating of {{gli|ice}} on the surface of an object. See {{gli|hard rime}} and {{gli|soft rime}}.}}

{{defn|A type of {{gli|radiosonde}} that is transported into the upper atmosphere, e.g. the {{gli|thermosphere}}, by rocket propulsion before being ejected and descending to the Earth's surface by parachute. Rocketsondes are used to make {{gli|atmospheric sounding|soundings}} at altitudes much higher than can usually be obtained by {{gli|weather balloon|balloon}} or aircraft. They can provide instantaneous vertical profiles for a number of meteorological variables (temperature, pressure, ozone concentration, wind speed and direction, etc.) as they descend through the layers of the atmosphere.}}

{{defn|An elongated, low-level {{gli|accessory cloud}} in the shape of a horizontal tube that appears to rotate slowly about its horizontal axis, and is associated with but completely detached from the {{gli|cloud base|base}} of a {{gli|cumulonimbus}} cloud above it. Though rare, roll clouds typically occur behind the {{gli|gust front}} along the leading edge of a {{gli|thunderstorm}} or {{gli|squall line}}; they are also sometimes associated with {{gli|cold fronts}}.}}

File:Roll-cloud.JPG

{{defn|A very large-scale atmospheric wave appearing on an upper-air isobaric analysis of the middle and upper {{gli|troposphere}}. Rossby waves consist of a series of {{gli|ridge|ridges}} and {{gli|trough|troughs}} with very long wavelengths (typically a few thousand kilometres) stretching around the Earth, principally in the middle latitudes. They are strongly linked to surface weather patterns.}}

{{defn|See {{gli|cyclonic rotation}}.}}

S

{{defn|See {{gli|col}}.}}

{{defn|A rating system used to classify {{gli|hurricanes}} ({{gli|tropical cyclones}} in the Western Hemisphere) into one of five categories according to the intensity of their {{gli|sustained wind|sustained winds}}, measured as the {{gli|maximum sustained wind}} speed averaged over a one-minute interval at an altitude of 10 meters above the surface. Category 1, the lowest rating on the scale, indicates average sustained wind speeds of {{convert|33|–|42|m/s|kn mph}}, where the lower limit is also used to define the distinction between a {{gli|tropical storm}} and a hurricane; Category 5, the highest rating, indicates wind speeds of {{convert|70|m/s|kn mph|sigfig=3}} or more.}}

{{defn|See {{gli|dust storm}}.}}

{{defn|Sharp, irregular grooves or ridges formed on a {{gli|snow}} surface by wind erosion, saltation of snow particles, and deposition, usually parallel to the prevailing winds. They are often found in the polar regions and in large, open areas such as frozen lakes in cold temperate regions.}}

{{defn|An {{gli|atmospheric sounding}} obtained from instruments on a meteorological satellite in orbit around the Earth.}}

{{defn|An independent {{gli|tornado}} that revolves around a larger, primary tornado (typically a very large and intense one) and interacts with the same {{gli|mesocyclone}}. Satellite tornadoes are distinct from the subvortices of a {{gli|multiple-vortex tornado}}, though they may still merge into their companion tornado.}}

{{defn|A {{gli|adiabat|curved line}} drawn on a thermodynamic diagram that traces the path of a {{gli|moisture|moisture-saturated}} {{gli|air parcel}} as it moves through the atmosphere {{gli|adiabatic process|adiabatically}}. Saturated parcels tend to behave very differently from dry parcels; the latter are instead described by a {{gli|dry adiabat}}.}}

{{defn|The maximum possible partial pressure exerted by a quantity of {{gli|water vapor}} in the atmosphere at a given temperature. Saturation vapor pressure increases non-linearly with air temperature according to the Clausius–Clapeyron relation, such that the vapor pressure in millibars at {{cvt|32|C|F}} is approximately double the value at {{cvt|21|C|F}}.}}

{{defn|See {{gli|pileus}}.}}

{{defn|The process by which particulate matter in the atmosphere is captured and removed by {{gli|precipitation}}.}}

{{defn|See {{gli|pannus}}.}}

{{defn|An onshore {{gli|local wind}} that blows from sea to land, a result of the more rapid warming of the land surface relative to the sea during the day. It blows in the opposite direction of a {{gli|land breeze}}, its nighttime counterpart in a {{gli|diurnal}} cycle of coastal winds caused by lateral differences in surface temperature between land and sea.}}

{{defn|{{gli|aerosol|Aerosol}} particles formed directly by the ocean, mostly by ejection into the atmosphere by bursting bubbles at the air-sea interface.}}

{{defn|The water {{gli|temperature}} of the surface layer of a sea or ocean, usually measured at a depth between {{convert|1|mm|in|2}} and {{convert|20|m|ft|-1}} beneath the surface. {{gli|air mass|Air masses}} in the atmosphere are strongly influenced by sea surface temperatures within a short distance of the shore.}}

{{defn|Any division of the year marked by changes in {{gli|weather}}, ecology, and the duration of daylight. Seasons result from the Earth's orbit around the Sun and its axial tilt relative to the ecliptic plane. In temperate and polar regions, four calendar-based seasons – {{gli|spring}}, {{gli|summer}}, {{gli|autumn}}, and {{gli|winter}} – are generally marked by significant changes in the intensity of sunlight that reaches the Earth's surface; these changes become less dramatic as one approaches the Equator, and so many tropical regions have only two or three seasons, such as a {{gli|wet season}} and a {{gli|dry season}}. In certain parts of the world, the term is also used to describe the timing of important ecological events, such as {{gli|hurricane season|hurricane seasons}}, flood seasons, and {{gli|wildfire}} seasons.}}

{{defn|The slow change (either an increase or a decrease) in the values of one or more climatic elements (e.g. temperature) that takes place over a long period of time, after fluctuations that occur over comparatively short periods have been eliminated.}}

{{defn|A stationary or standing wave (i.e. a wave that oscillates in time without moving through space) that occurs in an enclosed or semi-enclosed body of water, such as a lake or bay, or in the atmosphere, continuing to oscillate for some time after the force initiating its formation has ceased (occasionally as long as several days). Seiches may be caused by a variety of forces, including strong {{gli|winds}}, earthquakes, landslides, and sudden changes in {{gli|atmospheric pressure}}.}}

{{defn|The heat absorbed or transmitted by a substance during a change in temperature that is not accompanied by a change of phase (i.e. enthalpy) and which can be measured or "sensed", e.g. with a thermometer. Contrast {{gli|latent heat}}.}}

{{defn|The {{gli|temperature}} of the air or an object as it is felt or experienced by an individual. This may differ from the actual measured temperature for any of a number of reasons, e.g. as a result of {{gli|humidity}} (as with a {{gli|heat index}}) or {{gli|wind speed}} (as with {{gli|wind chill}}). Compare {{gli|apparent temperature}}.}}

{{defn|A type of {{gli|severe weather}} consisting of an especially strong or intense {{gli|thunderstorm}} accompanied by locally damaging {{gli|downdraft}} winds exceeding {{convert|50|kn|mph}}, heavy {{gli|rain}}, frequent {{gli|lightning}}, and/or large {{gli|hailstones}} with a diameter of at least {{convert|20|mm|in}}. Severe thunderstorms are often capable of producing {{gli|tornadoes}} as well.}}

{{defn|Any dangerous meteorological phenomena with the potential to cause damage on the ground surface, serious social disruption, or loss of human life. There are many types of severe weather, including strong {{gli|winds}}, excessive {{gli|precipitation}}, {{gli|thunderstorms}}, {{gli|tornadoes}}, {{gli|tropical cyclones}}, {{gli|blizzards}}, and {{gli|wildfire|wildfires}}. Some severe weather may be more or less typical of a given region during a given {{gli|season}}; other phenomena may be {{gli|extreme weather|atypical or unpredictable}}.}}

{{defn|See {{gli|atmospherics}}.}}

{{defn|The air {{gli|temperature}} as measured by a thermometer housed inside an instrument shelter, which allows air to circulate freely around the thermometer while sheltering it from the potentially confounding effects of direct {{gli|solar radiation}}, precipitation, and thermal energy emitted from the ground and surrounding objects. Shade temperature is a standard meteorological method for measuring air temperature.}}

{{defn|A diffuse illumination of the sky caused by a {{gli|lightning}} discharge in which the {{gli|lightning strike|bolt}} form of the discharge is not visible to an observer because of the presence of an obfuscating {{gli|cloud}}.}}

{{defn|A low, elongated, wedge-shaped {{gli|accessory cloud}} that occurs along a {{gli|gust front}}, often masking the boundary between {{gli|updraft|updrafts}} and {{gli|downdraft|downdrafts}}. Shelf clouds are associated with and attached to the base of a {{gli|cumulonimbus}} cloud, unlike {{gli|roll clouds}}, which are not attached.}}

{{defn|Any relatively small, short-wavelength ripple (i.e. a {{gli|trough}} or a {{gli|ridge}}) superimposed upon a {{gli|long wave|longer wave}} pattern in the planetary-scale movement of {{gli|air current|air currents}} within the middle and upper {{gli|troposphere}}. Short-wave troughs in particular are frequently associated with major cyclonic developments.}}

{{defn|A brief downpour of {{gli|precipitation}} (especially {{gli|rain}}, but also {{gli|snow}} or {{gli|hail}}) that starts and ends abruptly and typically lasts less than 10 minutes. Showers are characterized by rapid changes in intensity and are usually associated with {{gli|convective clouds}} (e.g. {{gli|cumulonimbus}}) which do not completely cover the sky, such that brightness is frequently evident during showers.}}

{{defn|In a {{gli|radiosonde}} observation, an altitude or elevation (other than a {{gli|mandatory level}}) for which temperature, pressure, and humidity are reported because temperature and/or {{gli|moisture content}} data at that level are sufficiently important or unusual to warrant the attention of the {{gli|weather forecasting|forecaster}}, or because they are required for the accurate portrayal of the observation.}}

{{defn|See {{gli|air-mass thunderstorm}}.}}

{{defn|The {{gli|storm spotting}} program of the U.S. {{gli|National Weather Service}}. Skywarn organizations have also been formed in Europe and Canada.}}

{{defn|A slurry mixture of small ice crystals (such as {{gli|snow}}) and liquid water. Slush forms when ice or snow melts.}}

{{defn|A type of solid {{gli|precipitation}} in the form of {{gli|ice crystals}} which precipitate from the atmosphere and subsequently undergo changes on the Earth's surface. Snow occurs when particles in the atmosphere attract supercooled water droplets, which nucleate and freeze into hexagonal crystals known as {{gli|snowflakes}}; upon reaching the ground it may then accumulate into snowpack or {{gli|snowdrifts}} and, over time, metamorphose by sintering, sublimation, and freeze-thaw mechanisms. Unless the local climate is cold enough to maintain persistent snow cover on the ground, snow typically melts seasonally.}}

{{defn|A phenomenon in which large snowballs form naturally as clumps of snow are blown along the ground by strong winds, growing larger as they accumulate material along the way.}}

{{defn|A region near the Great Lakes of North America where heavy snowfall in the form of {{gli|lake-effect snow}} is particularly common.}}

{{defn|A deposit of {{gli|snow}} sculpted by {{gli|wind}} into a mound during a {{gli|snowstorm}}.}}

{{defn|See {{gli|winter waterspout}}.}}

{{defn|A sudden, moderately heavy snowfall characterized by strong surface wind {{gli|gusts}} and {{gli|blowing snow}}. It is similar to a {{gli|blizzard}} but is more local in scale, and snow accumulations may or may not be significant.}}

{{ghat|Often used interchangeably with {{gli|winter storm}}.}}

{{defn|A type of {{gli|winter storm}} accompanied particularly by heavy precipitation in the form of {{gli|snow}}. Very large snowstorms with strong winds and meeting certain other criteria are called {{gli|blizzards}}.}}

{{defn|See {{gli|graupel}}.}}

{{defn|See {{gli|pyranometer}}.}}

{{defn|See {{gli|atmospheric sounding}}.}}

{{defn|See {{gli|weather balloon}}.}}

{{ghat|Also rocketsonde, research rocket, and suborbital rocket.}}

{{defn|A sub-orbital rocket carrying scientific instruments designed to record measurements and perform experiments in the upper atmosphere while in flight, usually reaching altitudes ranging from {{convert|48|to|145|km|mi}} above the surface of the Earth, i.e. higher than {{gli|weather balloons}} but lower than {{gli|weather satellites}}.[http://sites.wff.nasa.gov/code810/files/SRHB.pdf nasa.gov] NASA Sounding Rocket Program Handbook, June 2005, p. 1}}

{{defn|{{gli|sea spray|Sea spray}} blown from cresting waves during a {{gli|gale}}. This spray "drifts" in the direction of the gale and is distinct enough that it is sometimes used to judge {{gli|wind speed}} at sea.}}

{{defn|A weather phenomenon in which luminous plasma is created by a corona discharge at the tips of long, sharply pointed objects in a strong atmospheric electrical field, such as that generated by a {{gli|thunderstorm}}.}}

{{defn|See {{gli|cap cloud}}.}}

{{defn|Any influence upon the direction of movement of an atmospheric disturbance that is exerted by another aspect of the state of the atmosphere.{{cite web |url=https://glossary.ametsoc.org/wiki/Steering |website=AMS Glossary of Meteorology |title=steering |access-date=March 31, 2023}}}}

{{defn|Any disturbed state of an environment or {{gli|atmosphere}} especially affecting the ground surface and strongly implying {{gli|severe weather}}. Storms are characterized by significant disruptions to normal atmospheric conditions, which can result in strong {{gli|wind}}, heavy {{gli|precipitation}}, and/or {{gli|thunder}} and {{gli|lightning}} (as with a {{gli|thunderstorm}}), among other phenomena. They are created when a center of {{gli|low-pressure area|low pressure}} develops within a system of {{gli|high-pressure area|high pressure}} surrounding it.}}

{{defn|An {{gli|air mass}} which contains up and down {{gli|vertical draft|drafts}} in convective loops and which moves and reacts as a single entity. It functions as the smallest unit of a {{gli|storm}}-producing weather system.}}

{{defn|A National Climatic Data Center (NCDC) publication beginning in 1959 which details quality-controlled tornado and other severe weather summaries as the official NOAA record of such events.}}

{{defn|A type of underground bunker designed to protect the occupants from violent {{gli|severe weather}}, particularly {{gli|tornadoes}}.}}

{{defn|A type of {{gli|weather spotting}} in which observers watch for the approach of {{gli|storms}} and {{gli|severe weather}} and actively relay their findings to local meteorological authorities.}}

{{ghat|Also plough wind, thundergust, and hurricane of the prairie.}}

{{defn|Any very strong and potentially damaging {{gli|wind}} that lacks the rotational damage pattern associated with the winds of a {{gli|tornado}} and hence is said to blow in a "straight line". Straight-line winds commonly accompany the {{gli|outflow boundary|gust front}} of a {{gli|thunderstorm}} or originate with a {{gli|downburst}} and may {{gli|wind gust|gust}} as high as {{cvt|130|mph|kph}}.}}

{{defn|The second major layer of the Earth's {{gli|atmosphere}}, above the {{gli|troposphere}} and below the {{gli|mesosphere}}. The lower boundary of the stratosphere varies between {{cvt|7|and|20|km|mi}} above the Earth's surface, depending on latitude.}}

{{defn|See {{gli|quasi-biennial oscillation}}.}}

{{defn|See {{gli|parhelion}}.}}

{{defn|A meteorological phenomenon in which {{gli|rain}} falls while the sun is shining.}}

T

{{defn|A ragged band of {{gli|cloud}} and/or {{gli|fractus}} extending from a {{gli|wall cloud}} toward the precipitation core.}}

{{defn|A physical quantity expressing the thermal motion of a substance, such as a mass of air in the {{gli|atmosphere}}, and proportional to the average kinetic energy of the random microscopic motions of the substance's constituent particles. Temperature is measured with a {{gli|thermometer}} calibrated in one or more temperature scales: the Kelvin scale is the standard used in scientific contexts, but the Celsius and Fahrenheit scales are more commonly used in everyday contexts and for {{gli|weather forecasting}}.}}

{{defn|A physical quantity that describes in which direction and at what rate the {{gli|temperature}} changes within or across a particular system or location. It is typically expressed in units of degrees (on a particular temperature scale) per unit length; the SI unit is {{gli|Kelvin temperature scale|kelvin}} per meter (K/m).}}

{{defn|A format for reporting current and forecast weather conditions, particularly as such information relates to aviation. Standard TAFs are issued by major civil airfields at least four times a day (every six hours) and generally apply to a 24- or 30-hour period and an area within approximately {{convert|8|km|mi}} from the center of an airport runway complex. TAFs complement and use similar encoding to {{gli|METAR}} reports, but also take into account local geographic influences on weather.}}

{{defn|A column of rising air in the lower altitudes of the Earth's atmosphere. It is a form of atmospheric {{gli|updraft}} created by the uneven heating of the Earth's surface by {{gli|solar irradiance|solar radiation}}, and an example of {{gli|atmospheric convection}}.}}

{{defn|An instrument used to measure {{gli|temperature}} or a {{gli|temperature gradient}}.}}

{{defn|The sound produced as a result of the sudden thermal expansion of air within and surrounding the channel of a {{gli|lightning}} discharge. This expansion creates an audible supersonic shock wave that, depending on the listener's distance from the source, can range from a sharp, loud crack (sometimes called a thunderclap or peal of thunder) to a deep, sustained rumble. Thunder is a defining feature of {{gli|thunderstorms}}.}}

{{defn|A relatively weak {{gli|thunderstorm}}.}}

{{defn|A {{gli|storm}} characterized by the presence of {{gli|lightning}} and its acoustic effect on the Earth's atmosphere, known as {{gli|thunder}}. Thunderstorms result from the rapid upward movement of warm, moist air, often along a {{gli|front}}. They can develop in any geographic location but are most common in the mid-latitudes. They are usually accompanied by strong {{gli|winds}} and heavy {{gli|rain}}; especially strong or {{gli|severe thunderstorms}} can produce some of the most dangerous weather phenomena, including large {{gli|hail}}, {{gli|downbursts}}, and {{gli|tornadoes}}.}}

{{defn|A rapidly rotating column of air that is in contact with both a parent {{gli|cloud}} and the surface of the Earth. Tornadoes come in many shapes and sizes, and they are often visible in the form of a {{gli|funnel cloud|condensed funnel}} originating from the base of a {{gli|cumulonimbus}} cloud, usually during a {{gli|thunderstorm}}, with a cloud of rotating dust and debris beneath it. The most extreme tornadoes can achieve wind speeds of more than {{cvt|480|kph|mph}}, span more than {{cvt|3.2|km|mi}} in diameter, and stay on the ground for more than 100 km (dozens of miles) before dissipating.}}

File:A tornado near Anadarko, Oklahoma, on May 3, 1999.jpg

{{defn|An area of high reflectivity detected by {{gli|weather radar}} that is caused by large amounts of debris being lofted into the air, which is often indicative of a {{gli|tornado}}.}}

{{defn|The occurrence of multiple {{gli|tornadoes}} (typically at least six to ten) spawned by the same {{gli|synoptic scale meteorology|synoptic scale}} weather system, usually within the same day and in the same region.}}

{{defn|A period of continuous or nearly continuous {{gli|tornado}} activity consisting of a series of {{gli|tornado outbreak|tornado outbreaks}} spanning multiple days, with very few or no days lacking outbreaks.}}

{{defn|A rotation algorithm detected by {{gli|weather radar}} that indicates the likely presence of a strong {{gli|mesocyclone}} such as a {{gli|tornado}}. Such signatures can be used to track the location and development of a tornadic rotation within a larger storm.}}

{{defn|An amount of {{gli|precipitation}} that is too small to reliably or accurately measure.}}

{{ghat|Variously {{gli|hurricane}}, {{gli|typhoon}}, {{gli|tropical storm}}, cyclonic storm, or simply cyclone.}}

{{defn|A very large, {{gli|cyclone|rapidly rotating}} {{gli|storm}} system characterized by a {{gli|low-pressure area|low-pressure}} {{gli|eye|center}} surrounded by a closed low-level {{gli|atmospheric circulation}}, strong {{gli|wind|winds}}, and continuous spiral bands of {{gli|thunderstorms}} that produce heavy {{gli|rain}}. Tropical cyclones {{gli|tropical cyclogenesis|develop}} almost exclusively over and derive their strength from warm {{gli|tropics|tropical}} seas. The strongest systems can last for more than a week, span more than {{cvt|1600|km|mi|-2}} in diameter, and cause significant damage to coastal regions with powerful winds, {{gli|storm surges}}, and concentrated precipitation that leads to {{gli|flood|flooding}}. Depending on its location and strength, a tropical cyclone may be referred to by different names and categorized within a variety of classes.}}

{{defn|The process by which a {{gli|tropical cyclone}} develops and strengthens within the atmosphere. The mechanisms governing cyclone formation in the tropics are distinct from those that govern the development of {{gli|subtropical cyclone|subtropical}} and {{gli|extratropical cyclone|extratropical cyclones}}.}}

{{defn|The region of the Earth surrounding the Equator, generally delimited in latitude between the Tropic of Cancer (23°26' N) in the Northern Hemisphere and the Tropic of Capricorn (23°26' S) in the Southern Hemisphere.}}

{{defn|The boundary in the Earth's atmosphere between the {{gli|troposphere}} and the {{gli|stratosphere}}, on average situated approximately {{cvt|17|km|mi}} above equatorial regions and {{cvt|9|km|mi}} above the polar regions.}}

{{defn|The lowest layer of the Earth's {{gli|atmosphere}}, within which nearly all {{gli|weather}} phenomena occur. The troposphere contains approximately 75% of the atmosphere's total mass and 99% of its {{gli|water vapor}} and {{gli|aerosols}}. The average height of the troposphere above the Earth's surface varies between {{cvt|6|and|18|km|mi}} depending on latitude.}}

{{defn|An elongated region of relatively {{gli|low-pressure area|low atmospheric pressure}}, often associated with a {{gli|front}}. Troughs may exist at the surface or aloft or both; the lifting of moist air by {{gli|convergence|convergent winds}} usually causes clouds and precipitation to follow immediately behind a trough. Under certain conditions, troughs may alternate with {{gli|ridge|ridges}} in a high-amplitude pattern.}}

{{defn|Fluid motion characterized by chaotic changes in pressure and flow velocity, caused by excessive kinetic energy in parts of the fluid flow.}}

{{defn|no=1|The indirect illumination of the lower atmosphere caused by the scattering of sunlight when the Sun itself is not directly visible because it is below the horizon.}}

{{defn|no=2|The time period during which such illumination occurs, either between astronomical {{gli|dawn}} and sunrise or between sunset and astronomical {{gli|dusk}}.}}

{{defn|An acronym for Tactical Weather-Instrumented Sampling in/near Tornadoes EXperiment.}}

{{defn|The local name for a {{gli|tropical cyclone}} that occurs in the northwestern Pacific Ocean, between 180° and 100°E in the Northern Hemisphere.}}

U

{{defn|Any {{gli|air mass}} with high {{gli|convective instability}}, characterized by dramatic vertical {{gli|air current|air currents}}.}}

{{defn|An urban or metropolitan area within which air temperatures are significantly warmer than in surrounding rural or uninhabited areas as a result of human activities, especially the artificial modification of land surfaces and the generation of waste heat by energy usage. Urban heat islands can greatly influence precipitation, air quality, and the likelihood of certain weather phenomena in the vicinity of large cities, though not all cities have a distinct urban heat island.}}

V

{{defn|See {{gli|updraft}}.}}

{{defn|An estimate of the total mass of {{gli|precipitation}} contained in a {{gli|cloud}}, obtained by measuring the intensity of {{gli|weather radar|radar echoes}} returned from the atmosphere.}}

{{defn|The temperature of a moist {{gli|air parcel}} at which a theoretical dry air parcel would have a total {{gli|atmospheric pressure|pressure}} and {{gli|atmospheric density|density}} equal to those of the moist parcel.}}

{{defn|A set of regulations under which a pilot operates an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going, as opposed to {{gli|instrument flight rules}}, under which operation of the aircraft primarily occurs through referencing the onboard instruments rather than through visual reference to the ground and environs.}}

{{defn|A region within a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices are a major component of {{gli|turbulence}} and may be observed in many types of meteorological phenomena, including the winds surrounding a {{gli|tropical cyclone}}, {{gli|tornado}}, or {{gli|dust devil}}.}}

W

{{defn|A large, localized, persistent, and often abrupt lowering of {{gli|cloud}} that develops beneath the surrounding base of a {{gli|cumulonimbus}} cloud and from which {{gli|tornadoes}} sometimes form.}}

{{defn|A type of {{gli|front}} located at the leading edge of a warmer {{gli|air mass}} as it overtakes a cooler air mass that is moving more slowly in the same direction. Warm fronts lie within broader {{gli|trough|troughs}} of {{gli|low-pressure area|low pressure}} than {{gli|cold fronts}}, which sometimes follow them, and the temperature difference between the air masses they separate is often greater. {{gli|stratiform|Stratiform}} clouds, {{gli|fog}}, and steady {{gli|rain}} with occasional {{gli|thunderstorms}} often precede the boundary as it moves. In {{gli|surface weather analysis}}, warm fronts are symbolized by a red line with semicircles pointing in the direction of travel.}}

{{defn|Water in its gaseous state. Water vapor is ubiquitous in the atmosphere, being continuously generated by evaporation and removed by condensation, and plays a major role in numerous meteorological processes.}}

{{defn|The state of the {{gli|atmosphere}} at a given time and location. Weather is driven by a diverse set of naturally occurring phenomena, especially {{gli|atmospheric pressure|air pressure}}, {{gli|temperature}}, and {{gli|moisture}} differences between one place and another, most of which occur in the {{gli|troposphere}}.}}

{{defn|A high-altitude balloon used to carry scientific instruments into the atmosphere, which then measure, record, and transmit information about meteorological variables such as {{gli|atmospheric pressure}}, {{gli|temperature}}, {{gli|humidity}}, and {{gli|wind speed}} by means of a {{gli|radiosonde}} or other measurement device, often one which is expendable. Weather balloons are only feasible in the lower atmosphere and typically do not exceed {{convert|40|km|mi}} in altitude; higher parts of the atmosphere are generally studied with {{gli|sounding rockets}} or {{gli|weather satellite|satellites}}.}}

{{defn|See {{gli|explosive cyclogenesis}}.}}

{{defn|The application of science and technology to predict the conditions of the {{gli|atmosphere}} at a given time and location. Weather forecasts are made by collecting quantitative data about the current state of the atmosphere at a given place and then using {{gli|meteorology}} to project how the atmosphere will change. Forecasting is important to a wide variety of human activities, including business, agriculture, transportation, recreation and general health and safety, because it can be used to protect life and property.}}

{{defn|See {{gli|front}}.}}

{{defn|A map which displays various meteorological features across a particular area for a particular point or range of time. Weather maps often use symbols such as {{gli|station model|station models}} to conveniently present complicated meteorological data. They are used for both research and {{gli|weather forecasting}} purposes.}}

{{defn|no=1|In the United States, WSR-1, WSR-57, WSR-74, and {{gli|NEXRAD|WSR-88D}}.}}

{{defn|no=2|In Canada, the Canadian weather radar network (WKR and CWMN).}}

{{defn|The act of observing {{gli|weather}}, often on the ground, for the purpose of reporting to a larger group or organization, such as the U.S. {{gli|National Weather Service}}.}}

{{defn|Any facility, either on land or at sea, with instruments and equipment for measuring atmospheric conditions in order to provide information for {{gli|weather forecasting|weather forecasts}} and to study the {{gli|weather}} and/or {{gli|climate}}.}}

{{defn|An instrument (often an architectural ornament) used to indicate the {{gli|wind direction|direction}} of the {{gli|wind}}.}}

{{defn|A photographically adorned general interest weather magazine that frequently publishes articles on {{gli|tornadoes}} and other {{gli|severe weather}}.}}

{{defn|Any vertically oriented rotating {{gli|vortex}} of air that develops as a result of {{gli|turbulence|turbulent}} {{gli|air currents}} created by heating and flow gradients. Examples include major whirlwinds such as {{gli|tornadoes}}, {{gli|waterspouts}}, and {{gli|landspouts}} and minor whirlwinds such as {{gli|gustnadoes}} and {{gli|dust devils}}.}}

{{defn|See {{gli|dust devil}}.}}

{{defn|The bulk movement of air within the Earth's {{gli|atmosphere}}. Wind occurs on a wide range of scales, from very strong {{gli|thunderstorm}} flows lasting tens of minutes to milder local {{gli|breezes}} lasting a few hours to global {{gli|atmospheric circulation|atmospheric circulations}} caused by the differential heating of the Equator and the poles and the Earth's rotation. Winds are often referred to by their strength and {{gli|wind direction|direction}}; the many types of wind are classified according to their spatial scale, their {{gli|wind speed|speed}}, the types of forces that cause them, the regions in which they occur, and their effects.}}

{{defn|A meteorological index that estimates the effect of {{gli|wind speed}} on the {{gli|apparent temperature}} perceived by humans, particularly the decrease in human body temperature attributable to the movement of cold air. There is no universally agreed-upon formula for measuring or calculating wind chill, though it is commonly reported as a {{gli|temperature}}. It is usually defined only for air temperatures at or below {{cvt|10|C|F}} and wind speeds above {{cvt|4.8|km/h|mph}}.}}

{{defn|The direction from which a {{gli|wind}} originates; e.g. a northerly wind blows from the north to the south. Wind direction is usually reported using cardinal directions or in azimuth degrees measured clockwise from due north. Instruments such as {{gli|windsock|windsocks}}, {{gli|weather vane|weather vanes}}, and {{gli|anemometer|anemometers}} are commonly used to indicate wind direction.}}

{{defn|A brief increase in the {{gli|wind speed|speed}} of the {{gli|wind}}, usually lasting less than 20 seconds. Gusts are more transient than {{gli|squall|squalls}}. They are usually only reported by weather stations when the maximum or peak wind speed exceeds the average wind speed by {{convert|10|–|15|kn|mph}}.}}

{{ghat|Sometimes used interchangeably with {{gli|wind gradient}}.}}

{{defn|Any difference in {{gli|wind speed}} and/or {{gli|wind direction|direction}} over a relatively short distance in the {{gli|atmosphere}}. Atmospheric wind shear is normally described as either {{gli|vertical wind shear|vertical}} or {{gli|horizontal wind shear|horizontal}}.}}

{{defn|The measured speed of the air comprising a {{gli|wind}}. Changes in wind speed are often caused by {{gli|air parcel|air parcels}} being exposed to {{gli|pressure gradient|pressure}} and {{gli|temperature gradient|temperature gradients}} in the atmosphere. Wind speed is measured with an {{gli|anemometer}}, but may also be less precisely classified using the {{gli|Beaufort scale}}.}}

{{defn|Any {{gli|storm}} that produces or is characterized by very strong {{gli|winds}}.}}

{{ghat|Often used interchangeably with {{gli|snowstorm}}.}}

{{defn|no=1|Any {{gli|storm}} which occurs during the local {{gli|winter}}.}}

{{defn|no=2|Any meteorological event in which varieties of {{gli|precipitation}} which can only occur at low temperatures are formed, such as {{gli|snow}}, {{gli|sleet}}, or {{gli|freezing rain}}. Such events are not necessarily restricted to the winter season but may occur in late {{gli|autumn}} or early {{gli|spring}}, or very rarely in the {{gli|summer}}, as well.}}

X

Y

Z

{{defn|See {{gli|sastrugi}}.}}

References

External links

{{cite web|url=http://glossary.ametsoc.org/wiki/Main_Page|title=AMS Glossary|publisher=American Meteorological Society}}

meteorology

Category:Wikipedia glossaries using description lists