Severe weather#High winds

Meteorologists have generally defined severe weather as any aspect of the weather that poses risks to life or property or requires the intervention of authorities. A narrower definition of severe weather is any weather phenomenon relating to severe thunderstorms.{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?id=severe-storm1|title=Severe storm|publisher=American Meteorological Society|access-date=4 February 2010|url-status=dead|archive-url=https://web.archive.org/web/20051026171035/http://amsglossary.allenpress.com/glossary/search?id=severe-storm1|archive-date=26 October 2005}}

According to the World Meteorological Organization (WMO), severe weather can be categorized into two groups: general severe weather and localized severe weather. Nor'easters, European wind storms, and the phenomena that accompany them form over wide geographic areas. These occurrences are classified as general severe weather. Downbursts and tornadoes are more localized and therefore have a more limited geographic effect. These forms of weather are classified as localized severe weather.

The term severe weather is technically not the same phenomenon as extreme weather. Extreme weather describes unusual weather events that are at the extremes of the historical distribution for a given area.{{cite web |url=http://www.grida.no/publications/other/ipcc_tar/?src=/CLIMATE/IPCC_TAR/wg1/518.htm |title=IPCC Third Assessment Report – Climate Change 2001 – Complete online versions | GRID-Arendal – Publications – Other |publisher=Grida.no |access-date=20 November 2013 |url-status=dead |archive-url=https://web.archive.org/web/20120928074318/http://www.grida.no/publications/other/ipcc_tar/?src=%2FCLIMATE%2FIPCC_TAR%2Fwg1%2F518.htm |archive-date=28 September 2012 }}

File:CAPE vs SHEAR.svg and vertical wind shear values.|left]]

{{See also|Extreme weather#Causes and attribution}}

Organized severe weather occurs under the same conditions that generate ordinary thunderstorms: atmospheric moisture, lift (often from thermals), and instability.{{cite web |url=http://www.spc.noaa.gov/faq |title=Storm Prediction Center Frequently Asked Questions (FAQ) |publisher=Spc.noaa.gov |date=16 July 2008 |access-date=5 December 2009 |archive-date=25 August 2009 |archive-url=https://web.archive.org/web/20090825020652/http://www.spc.noaa.gov/faq/ |url-status=live }} A wide variety of conditions cause severe weather. Several factors can convert thunderstorms into severe weather. For example, a pool of cold air aloft may aid in the development of large hail from an otherwise innocuous-appearing thunderstorm. The most severe hail and tornadoes are produced by supercell thunderstorms, and the worst downbursts and derechos (straight-line winds) are produced by bow echoes. Both of these types of storms tend to form in environments with high wind shear.

Floods, hurricanes, tornadoes, and thunderstorms are considered to be the most destructive weather-related natural disasters. Although these weather phenomena are all related to cumulonimbus clouds, they form and develop under different conditions and geographic locations. The relationship between these weather events and their formation requirements is used to develop models to predict the most frequent and possible locations. This information is used to notify affected areas and save lives.

File:Comp-rcm.png

Severe thunderstorms can be assessed in three different categories. These are "approaching severe", "severe", and "significantly severe".

Approaching severe is defined as hail between {{convert|1/2|to|1|in|sp=us}} diameter or winds between 50 and 58 mph (50 knots, 80–93 km/h). In the United States, such storms will usually warrant a Significant Weather Alert.{{cite web |url=http://www.srh.noaa.gov/jetstream//append/glossary_a.htm |title=NWS JetStream – Weather Glossary: A's |publisher=Srh.noaa.gov |date=8 June 2011 |access-date=20 November 2013 |archive-date=24 September 2013 |archive-url=https://web.archive.org/web/20130924210751/http://www.srh.noaa.gov/jetstream/append/glossary_a.htm |url-status=live }}

Severe is defined as hail {{convert|1|to|2|in|sp=us}} diameter, winds {{convert|58|to|75|mph}}, or a tornado.{{cite web |url=http://www.weather.gov/oneinchhail/ |title=Why One Inch Hail Criterion? |publisher=National Weather Service |access-date=29 May 2010 |archive-url=https://web.archive.org/web/20100430022837/http://www.weather.gov/oneinchhail/ |archive-date=30 April 2010 |url-status=dead }}

Significant severe is defined as hail {{convert|2|in|sp=us}} in diameter or larger, winds 75 mph (65 knots, 120 km/h) or more, or a tornado of strength EF2 or stronger.{{cite web|url=http://www.spc.noaa.gov/climo/online/rda|title=Online Severe Weather Climatology – Radar Coverage Areas|publisher=Storm Prediction Center|date=6 October 2007|access-date=29 May 2010|archive-date=30 May 2010|archive-url=https://web.archive.org/web/20100530002617/http://www.spc.noaa.gov/climo/online/rda/|url-status=live}}

Both severe and significant severe events warrant a severe thunderstorm warning from the United States National Weather Service (excludes flash floods), the Environment Canada, the Australian Bureau of Meteorology, the Meteorological Service of New Zealand and the Meteorological Office UK, if the event occurs in those countries. If a tornado is occurring (a tornado has been seen by spotters) or is imminent (Doppler weather radar has observed strong rotation in a storm, indicating an incipient tornado), the severe thunderstorm warning will be superseded by a tornado warning in the United States and Canada.{{cite web|last=Edwards|first=Roger|title=The Online Tornado FAQ: Frequently Asked Questions about Tornadoes|url=http://www.spc.noaa.gov/faq/tornado/|publisher=Storm Prediction Center, NOAA|access-date=29 March 2012|date=23 March 2012|archive-date=2 March 2012|archive-url=https://web.archive.org/web/20120302230203/http://www.spc.noaa.gov/faq/tornado/|url-status=live}}

A severe weather outbreak is typically considered to be when ten or more tornadoes, some of which will likely be long-tracked and violent, and many large hail or damaging wind reports occur within one or more consecutive days. Severity is also dependent on the size of the geographic area affected, whether it covers hundreds or thousands of square kilometers.Guyer, Jared. "SPC Web Feedback – Outbreaks." Message to the author. 14 June 2007. E-mail.

{{Clear}}

{{Main|Wind|Beaufort scale}}

File:Thunderstorm panorama.jpg, which can precede the onset of high winds]]

High winds are known to cause damage, depending upon their strength.

Wind speeds as low as {{convert|23|kn|km/h}} may lead to power outages when tree branches fall and disrupt power lines.{{cite book|author1=Hans Dieter Betz|author2=Ulrich Schumann|author3=Pierre Laroche|year=2009|url=https://books.google.com/books?id=U6lCL0CIolYC&pg=PA187|title=Lightning: Principles, Instruments and Applications|publisher=Springer|pages=202–203|isbn=978-1-4020-9078-3|access-date=13 May 2009|archive-date=30 October 2023|archive-url=https://web.archive.org/web/20231030003909/https://books.google.com/books?id=U6lCL0CIolYC&pg=PA187#v=onepage&q&f=false|url-status=live}} Some species of trees are more vulnerable to winds. Trees with shallow roots are more prone to uproot, and brittle trees such as eucalyptus, sea hibiscus, and avocado are more prone to branch damage.{{cite web|author=Derek Burch|url=http://edis.ifas.ufl.edu/EP042|title=How to Minimize Wind Damage in the South Florida Garden|publisher=University of Florida|date=26 April 2006|access-date=13 May 2009|archive-date=20 June 2012|archive-url=https://web.archive.org/web/20120620125721/http://edis.ifas.ufl.edu/ep042|url-status=live}}

Wind gusts may cause poorly designed suspension bridges to sway. When wind gusts harmonize with the frequency of the swaying bridge, the bridge may fail as occurred with the Tacoma Narrows Bridge in 1940.{{cite book|author=T. P. Grazulis|year=2001|url=https://books.google.com/books?id=N6Tiz_7VmJoC&q=wind+sensitivity+of+powerlines&pg=PA127|title=The tornado|publisher=University of Oklahoma Press|pages=126–127|isbn=978-0-8061-3258-7|access-date=13 May 2009|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812042611/https://books.google.com/books?id=N6Tiz_7VmJoC&q=wind+sensitivity+of+powerlines&pg=PA127|url-status=live}}

Hurricane-force winds, caused by individual thunderstorms, thunderstorm complexes, derechos, tornadoes, extratropical cyclones, or tropical cyclones can destroy mobile homes and structurally damage buildings with foundations. Winds of this strength due to downslope winds off terrain have been known to shatter windows and sandblast paint from cars.{{cite web|url=http://www.ucar.edu/communications/factsheets/winds.html|access-date=16 June 2009|date=10 April 2000|author=Rene Munoz|publisher=University Corporation for Atmospheric Research|title=Boulder's downslope winds|url-status=dead|archive-url=https://web.archive.org/web/20120319015922/http://www.ucar.edu/communications/factsheets/winds.html|archive-date=19 March 2012}}

Once winds exceed {{convert|135|kn|km/h}} within strong tropical cyclones and tornadoes, homes completely collapse, and significant damage is done to larger buildings. Total destruction to man-made structures occurs when winds reach {{convert|175|kn|km/h}}. The Saffir–Simpson scale for cyclones and Enhanced Fujita scale (TORRO scale in Europe) for tornadoes were developed to help estimate wind speed from the damage they cause.{{cite web|author=National Hurricane Center|title=Saffir-Simpson Hurricane Scale Information|publisher=National Oceanic and Atmospheric Administration|date=22 June 2006|url=http://www.nhc.noaa.gov/aboutsshs.shtml|access-date=25 February 2007|archive-date=22 June 2012|archive-url=https://web.archive.org/web/20120622174847/http://www.nhc.noaa.gov/aboutsshws.php|url-status=live}}{{cite web|title=Enhanced F Scale for Tornado Damage|author=Storm Prediction Center|url=http://www.spc.noaa.gov/efscale/ef-scale.html|date=1 February 2007|access-date=13 May 2009|archive-date=11 July 2012|archive-url=https://web.archive.org/web/20120711091501/http://www.spc.noaa.gov/efscale/ef-scale.html|url-status=live}}

{{Main|Tornado}}

File:F5 tornado Elie Manitoba 2007.jpg, Canada, in 2007]]

A dangerous rotating column of air in contact with both the surface of the earth and the base of a cumulonimbus cloud (thundercloud) or a cumulus cloud, in rare cases. Tornadoes come in many sizes but typically form a visible condensation funnel whose narrowest end reaches the earth and surrounded by a cloud of debris and dust.{{cite journal |last=Renno |first=Nilton O. |title=A thermodynamically general theory for convective vortices |journal=Tellus A |volume=60 |issue=4 |pages=688–99 |date=August 2008 |url=http://vortexengine.ca/misc/Renno_2008.pdf |doi=10.1111/j.1600-0870.2008.00331.x |bibcode=2008TellA..60..688R |hdl=2027.42/73164 |hdl-access=free |access-date=20 August 2009 |archive-date=9 October 2022 |archive-url=https://ghostarchive.org/archive/20221009/http://vortexengine.ca/misc/Renno_2008.pdf |url-status=live }}

Tornadoes' wind speeds generally average between {{convert|40|mph|km/h}} and {{convert|110|mph|km/h}}. They are approximately {{convert|250|ft|m}} across and travel a few miles (kilometers) before dissipating. Some attain wind speeds in excess of {{convert|300|mph|km/h}}, may stretch more than two miles (3.2 km) across, and maintain contact with the ground for dozens of miles (more than 100 km).{{cite web |url=http://www.spc.noaa.gov/faq/tornado |title=The Online Tornado FAQ |access-date=8 September 2006 |last=Edwards |first=Roger |date=4 April 2006 |publisher=Storm Prediction Center |archive-date=2 March 2012 |archive-url=https://web.archive.org/web/20120302230203/http://www.spc.noaa.gov/faq/tornado/ |url-status=live}}A tornado can pose threats to both humans and buildings. {{cite web |url=http://cswr.org/dow/DOW.htm |title=Doppler On Wheels |access-date=29 December 2006 |publisher=Center for Severe Weather Research |year=2006 |url-status=dead |archive-url=https://web.archive.org/web/20070205124033/http://www.cswr.org/dow/dow.htm |archive-date=5 February 2007 }}{{cite web |url=http://mattcuttsalerts.com/tornado-warnings/ |title=Tornado Warnings infographic |access-date=18 July 2013 |publisher=MCA |date=18 July 2013 |url-status=usurped |archive-url=https://web.archive.org/web/20130716172215/http://mattcuttsalerts.com/tornado-warnings/ |archive-date=16 July 2013}} The Enhanced Fujita Scale and the TORRO Scale are two examples of scales used to rate the strength, intensity and/or damage of a tornado.

Tornadoes, despite being one of the most destructive weather phenomena, are generally short-lived. A long-lived tornado generally lasts no more than an hour, but some have been known to last for 2 hours or longer (for example, the Tri-State Tornado). Due to their relatively short duration, less information is known about the development and formation of tornadoes.{{cite web |title=Tornadoes |url=http://www.windows.ucar.edu/tour/link%3D/earth/Atmosphere/tornado.html%26edu%3Dhigh |date=1 August 2008 |access-date=3 August 2009 |archive-date=12 October 2009 |archive-url=https://web.archive.org/web/20091012142147/http://www.windows.ucar.edu/tour/link%3D/earth/Atmosphere/tornado.html%26edu%3Dhigh |url-status=live}}

{{Main|Waterspout}}

File:Great Lakes Waterspouts.jpg

Waterspouts are generally defined as tornadoes or non-supercell tornadoes that develop over bodies of water.{{cite web |url=http://amsglossary.allenpress.com/glossary/search?p=1&query=Waterspout |title=AMS Glossary |publisher=Amsglossary.allenpress.com |access-date=5 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20080620115657/http://amsglossary.allenpress.com/glossary/search?p=1&query=waterspout |archive-date=20 June 2008 }}

Waterspouts typically do not do much damage because they occur over open water, but they are capable of traveling over land. Vegetation, weakly constructed buildings, and other infrastructure may be damaged or destroyed by waterspouts. Waterspouts do not generally last long over terrestrial environments as the friction produced easily dissipates the winds. Strong horizontal winds will cause waterspouts to dissipate as they disturb the vortex.{{cite web |url=http://www.erh.noaa.gov/ilm/beach/waterspouts/waterspouts_information.shtml |title=Waterspout Information – NWS Wilmington, North Carolina |publisher=Erh.noaa.gov |date=14 January 2007 |access-date=5 December 2009 |archive-date=11 June 2011 |archive-url=https://web.archive.org/web/20110611214152/http://www.erh.noaa.gov/ilm/beach/waterspouts/waterspouts_information.shtml |url-status=live }} While not generally as dangerous as "classic" tornadoes, waterspouts can overturn boats, and they can cause severe damage to larger ships.

{{Main|Downburst|Derecho}}

Downbursts are created within thunderstorms by significantly rain-cooled air, which, upon reaching ground level, spreads out in all directions and produce strong winds. Unlike winds in a tornado, winds in a downburst are not rotational but are directed outwards from the point where they strike land or water.File:Microburstnasa.JPG "Dry downbursts" are associated with thunderstorms with very little precipitation,{{cite web |author1=Fernando Caracena |author2=Ronald L. Holle |author3=Charles A. Doswell III |name-list-style=amp |url=http://www.cimms.ou.edu/~doswell/microbursts/Handbook.html |title=Microbursts: A Handbook for Visual Identification |date=26 June 2002 |access-date=9 July 2008 |archive-date=24 November 2005 |archive-url=https://web.archive.org/web/20051124121208/http://www.cimms.ou.edu/~doswell/microbursts/Handbook.html |url-status=live}} while wet downbursts are generated by thunderstorms with large amounts of rainfall. Microbursts are very small downbursts with winds that extend up to 2.5 miles (4 km) from their source, while macrobursts are large-scale downbursts with winds that extend in excess of 2.5 miles (4 km).{{cite web |author=Fernando Caracena |publisher=NOAA/Forecast Systems Laboratory |url=http://www-frd.fsl.noaa.gov/mab/microburst/micro_course.html |title=Microburst |access-date=16 January 2015 |year=2015 |url-status=dead |archive-url=https://web.archive.org/web/20141219103329/http://www-frd.fsl.noaa.gov/mab/microburst/micro_course.html |archive-date=19 December 2014}} The heat burst is created by vertical currents on the backside of old outflow boundaries and squall lines where rainfall is lacking. Heat bursts generate significantly higher temperatures due to the lack of rain-cooled air in their formation.{{cite news |title=Oklahoma "heat burst" sends temperatures soaring |work=USA Today |url=https://www.usatoday.com/weather/wheatbst.htm |access-date=9 May 2007 |date=8 July 1999 |archive-date=2 February 1999 |archive-url=https://web.archive.org/web/19990202180106/https://www.usatoday.com/weather/wheatbst.htm |url-status=live}} Derechos are longer, usually stronger, forms of downburst winds characterized by straight-lined windstorms.{{cite web| url=http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm| title=About Derechos| publisher=Storm Prediction Center, NCEP, NWS, NOAA Web Site| first=Stephen F.| last=Corfidi| author2=Robert H. Johns| author3=Jeffry S. Evans| date=3 December 2013| access-date=15 January 2014| archive-date=20 January 2021| archive-url=https://web.archive.org/web/20210120002540/https://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm| url-status=live}}{{cite book |title=Extreme Weather |last=Mogil |first=H. Michael |year=2007 |publisher=Black Dog & Leventhal Publisher |location=New York |isbn=978-1-57912-743-5 |pages=[https://archive.org/details/extremeweatherun0000mogi/page/210 210–211] |url=https://archive.org/details/extremeweatherun0000mogi/page/210 }}

Downbursts create vertical wind shear or microbursts, which are dangerous to aviation.{{cite web |author=National Aeronautics and Space Administration Langley Air Force Base |url=http://oea.larc.nasa.gov/PAIS/Windshear.html |title=Making the Skies Safer From Windshear |date=June 1992 |access-date=22 October 2006 |url-status=dead |archive-url=https://web.archive.org/web/20100329221032/http://oea.larc.nasa.gov/PAIS/Windshear.html |archive-date=29 March 2010 }} These convective downbursts can produce damaging winds, lasting 5 to 30 minutes, with wind speeds as high as {{convert|168|mph|m/s|abbr=on}}, and cause tornado-like damage on the ground. Downbursts also occur much more frequently than tornadoes, with ten downburst damage reports for every one tornado.{{cite web|last=National Weather Service Forecast Office, Columbia, South Carolina |title=Downbursts |url=http://www.erh.noaa.gov/cae/svrwx/downburst.htm |access-date=29 March 2012 |date=5 May 2010 |url-status=dead |archive-url=https://web.archive.org/web/20120813214806/http://www.erh.noaa.gov/cae/svrwx/downburst.htm |archive-date=13 August 2012 }}

File:Pehrcn07212003.gif over Pennsylvania with a trailing squall line]]

{{Main|Squall line|Severe thunderstorm|Bow echo|Derecho}}

A squall line is an elongated line of severe thunderstorms that can form along or ahead of a cold front.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=squall-line1|title=Squall line|year=2009|access-date=14 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20081217175139/http://amsglossary.allenpress.com/glossary/search?id=squall-line1|archive-date=17 December 2008}}{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=prefrontal-squall-line1|title=Prefrontal squall line|year=2009|access-date=14 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20070817224959/http://amsglossary.allenpress.com/glossary/search?id=prefrontal-squall-line1|archive-date=17 August 2007}} The squall line typically contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes or waterspouts.{{cite web|year=2008 |url=http://www.ofcm.gov/slso/pdf/slsochp2.pdf |title=Chapter 2: Definitions |pages=2–1 |publisher=NOAA |access-date=3 May 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090506002006/http://www.ofcm.gov/slso/pdf/slsochp2.pdf |archive-date=6 May 2009 }} Severe weather in the form of strong straight-line winds can be expected in areas where the squall line forms a bow echo, in the farthest portion of the bow.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=bow+echo&submit=Search|title=Bow echo|year=2009|access-date=14 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20110606103620/http://amsglossary.allenpress.com/glossary/search?p=1&query=bow+echo&submit=Search|archive-date=6 June 2011}} Tornadoes can be found along waves within a line echo wave pattern (LEWP) where mesoscale low-pressure areas are present.{{cite book|year=2009|url=http://amsglossary.allenpress.com/glossary/search?id=line-echo-wave-pattern1|title=Line echo wave pattern|publisher=American Meteorological Society|isbn=978-1-878220-34-9|access-date=3 May 2009|url-status=dead|archive-url=https://web.archive.org/web/20080924175030/http://amsglossary.allenpress.com/glossary/search?id=line-echo-wave-pattern1|archive-date=24 September 2008}} Intense bow echoes responsible for widespread, extensive wind damage are called derechos, and move quickly over large territories. A wake low or a mesoscale low-pressure area forms behind the rain shield (a high pressure system under the rain canopy) of a mature squall line and is sometimes associated with a heat burst.{{cite book |title= Heat burst |publisher= American Meteorological Society |year= 2009 |url=http://amsglossary.allenpress.com/glossary/search?id=heat-burst1 |isbn= 978-1-878220-34-9 |access-date= 14 June 2009 |url-status= dead |archive-url=https://web.archive.org/web/20110606102146/http://amsglossary.allenpress.com/glossary/search?id=heat-burst1 |archive-date= 6 June 2011 }}

Squall lines often cause severe straight-line wind damage, and most non-tornadic wind damage is caused from squall lines.{{cite web|last=National Weather Forecast Office, Louisville, Kentucky|title=Structure and Evolution of Squall Line and Bow Echo Convective Systems|url=http://www.crh.noaa.gov/lmk/soo/docu/bowecho.php|publisher=NOAA|access-date=29 March 2012|date=31 August 2010|archive-date=16 November 2014|archive-url=https://web.archive.org/web/20141116214959/http://www.crh.noaa.gov/lmk/soo/docu/bowecho.php|url-status=live}} Although the primary danger from squall lines is straight-line winds, some squall lines also contain weak tornadoes.

File:Hurricane Isabel from ISS.jpg (2003) as seen from orbit during Expedition 7 of the International Space Station]]

{{Main|Tropical cyclone}}

Very high winds can be caused by mature tropical cyclones (called hurricanes in the United States and Canada and typhoons in eastern Asia). A tropical cyclone's heavy surf created by such winds may cause harm to marine life either close to or upon the surface of the water, such as coral reefs.{{cite journal|url=http://bbp.amnh.org/Newsletters/Issue3/hurricanes.html|title=Hurricanes and Coral Reef Communities|author=Dan Brumbaugh|journal=BBP in Brief|issue=3|date=October 2004|access-date=18 August 2009|archive-date=12 August 2011|archive-url=https://web.archive.org/web/20110812063526/http://bbp.amnh.org/Newsletters/Issue3/hurricanes.html|url-status=live}} Coastal regions usually take more serious wind damage than inland, due to rapid dissipation upon landfall, though heavy rain from their remnants may flood either.

File:Intense Nor'Easter over the N. Alantic on Mar 26, 2014.png Imagery of an intense Nor'Easter that impacted the North East US on 26 March 2014 and produced recorded gusts of 101mph+]]

{{Main|Extratropical cyclone}}

Severe local windstorms in Europe that develop from winds off the North Atlantic. These windstorms are commonly associated with the destructive extratropical cyclones and their low pressure frontal systems.{{cite web |url=http://www.pandowae.de/?q=en/node/36 |archive-url=https://archive.today/20130211225215/http://www.pandowae.de/?q=en/node/36 |url-status=dead |archive-date=11 February 2013 |title=European Windstorms | PANDOWAE |publisher=Pandowae.de |access-date=5 December 2009 }} European windstorms occur mainly in the seasons of autumn and winter.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=adiabatic-process1|title=Adiabatic process|access-date=18 August 2009|year=2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20071017213229/http://amsglossary.allenpress.com/glossary/search?id=adiabatic-process1|archive-date=17 October 2007}} Severe European windstorms are often characterized by heavy precipitation as well.

A synoptic-scale extratropical storm along the upper East Coast of the United States and Atlantic Canada is called a Nor'easter. They are so named because their winds come from the northeast, especially in the coastal areas of the Northeastern United States and Atlantic Canada. More specifically, it describes a low-pressure area whose center of rotation is just off the upper East Coast and whose leading winds in the left forward quadrant rotate onto land from the northeast. Nor'easters may cause coastal flooding, coastal erosion, heavy rain or snow, and hurricane-force winds. The precipitation pattern of Nor'easters is similar to other mature extratropical storms. Nor'easters can cause heavy rain or snow, either within their comma-head precipitation pattern or along their trailing cold or stationary front. Nor'easters can occur at any time of the year but are mostly known for their presence in the winter season.{{cite web|title=Nor'easters|year=2006|access-date=22 January 2008|url=http://www.mcwar.org/articles/noreasters/NorEasters.html |archive-url=https://web.archive.org/web/20071009034304/http://www.mcwar.org/articles/noreasters/NorEasters.html |archive-date = 9 October 2007}}

{{Main|Dust storm}}

A dust storm is an unusual form of windstorm that is characterized by the existence of large quantities of sand and dust particles carried by the wind.{{cite web |url=http://amsglossary.allenpress.com/glossary/search?p=1&query=DustStorm |title=AMS Glossary |publisher=Amsglossary.allenpress.com |access-date=5 December 2009 |archive-url=https://web.archive.org/web/20110606103837/http://amsglossary.allenpress.com/glossary/search?p=1&query=DustStorm |archive-date=6 June 2011 |url-status=dead }} Dust storms frequently develop during periods of droughts, or over arid and semi-arid regions.

File:Sandstorm in Al Asad, Iraq.jpg) is close to enveloping a military camp as it rolls over Al Asad Airbase, Iraq, just before nightfall on 27 April 2005.]]

Dust storms have numerous hazards and are capable of causing deaths. Visibility may be reduced dramatically, so risks of vehicle and aircraft crashes are possible. Additionally, the particulates may reduce oxygen intake by the lungs,{{cite web |url=http://www.health.nsw.gov.au/factsheets/environmental/dust_storms.html |title=Dust storms Factsheet – NSW Department of Health |publisher=Health.nsw.gov.au |access-date=5 December 2009 |archive-date=26 November 2009 |archive-url=https://web.archive.org/web/20091126004910/http://www.health.nsw.gov.au/factsheets/environmental/dust_storms.html |url-status=live }} potentially resulting in suffocation. Damage can also be inflicted upon the eyes due to abrasion.{{cite web |url=http://www.nws.noaa.gov/om/brochures/duststrm.htm |title=Dust Storm Safety |publisher=Nws.noaa.gov |access-date=5 December 2009 |archive-date=8 March 2009 |archive-url=https://web.archive.org/web/20090308011202/http://nws.noaa.gov/om/brochures/duststrm.htm |url-status=live }}

Dust storms cause many issues for agricultural industries as well. Soil erosion is one of the most common hazards and decreases arable lands. Dust and sand particles can cause severe weathering of buildings and rock formations. Nearby bodies of water may be polluted by settling dust and sand, killing aquatic organisms. Decrease in exposure to sunlight can affect plant growth, as well as decrease in infrared radiation may cause decreased temperatures.

{{Main|Wildfire}}

{{See also|Dry lightning}}

File:Wildfire in Yellowstone NP produces Pyrocumulus cloud.jpg produces a pyrocumulus cloud.]]

The most common cause of wildfires varies throughout the world. In the United States, Canada, and Northwest China, lightning is the major source of ignition. In other parts of the world, human involvement is a major contributor. For instance, in Mexico, Central America, South America, Africa, Southeast Asia, Fiji, and New Zealand, wildfires can be attributed to human activities such as animal husbandry, agriculture, and land-conversion burning. Human carelessness is a major cause of wildfires in China and in the Mediterranean Basin. In Australia, the source of wildfires can be traced to both lightning strikes and human activities such as machinery sparks and cast-away cigarette butts."{{cite web|last=Krock|first=Lexi|title=The World on Fire|publisher=NOVA online – Public Broadcasting System (PBS)|access-date=13 July 2009|date=June 2002|url=https://www.pbs.org/wgbh/nova/fire/world.html|archive-date=27 October 2009|archive-url=https://web.archive.org/web/20091027041902/http://www.pbs.org/wgbh/nova/fire/world.html|url-status=live}} Wildfires have a rapid forward rate of spread (FROS) when burning through dense, uninterrupted fuels.{{cite web|url=http://www.flash.org/resources/files/WildfireBrochure.pdf|title=Protecting Your Home From Wildfire Damage|publisher=Florida Alliance for Safe Homes (FLASH)|access-date=3 March 2010|page=5|archive-date=19 July 2011|archive-url=https://web.archive.org/web/20110719000918/http://www.flash.org/resources/files/WildfireBrochure.pdf|url-status=dead}} They can move as fast as {{Convert|10.8|km/h|mph|sp=us}} in forests and {{convert|22|km/h|mph|sp=us}} in grasslands.Billing, 5–6 Wildfires can advance tangential to the main front to form a flanking front, or burn in the opposite direction of the main front by backing.Graham, et al.., 12

Wildfires may also spread by jumping or spotting as winds and vertical convection columns carry firebrands (hot wood embers) and other burning materials through the air over roads, rivers, and other barriers that may otherwise act as firebreaks.{{cite web | url = http://ngm.nationalgeographic.com/2008/07/fire-season/shea-text.html | title = Under Fire | last = Shea | first = Neil | publisher = National Geographic | date = July 2008 | access-date = 8 December 2008 | archive-date = 15 February 2009 | archive-url = https://web.archive.org/web/20090215065522/http://ngm.nationalgeographic.com/2008/07/fire-season/shea-text.html | url-status = dead }}Graham, et al.., 16. Torching and fires in tree canopies encourage spotting, and dry ground fuels that surround a wildfire are especially vulnerable to ignition from firebrands.Graham, et al.., 9, 16. Spotting can create spot fires as hot embers and firebrands ignite fuels downwind from the fire. In Australian bushfires, spot fires are known to occur as far as {{convert|10|km|0|sp=us}} from the fire front.Billing, 5 Since the mid-1980s, earlier snowmelt and associated warming has also been associated with an increase in length and severity of the wildfire season in the Western United States.{{Cite journal | doi = 10.1126/science.1128834 |date=Aug 2006 |author1=Westerling, Al |author2=Hidalgo, Hg |author3=Cayan |author4=Swetnam, Tw | title = Warming and earlier spring increase western U.S. Forest wildfire activity | volume = 313 | issue = 5789 | pages = 940–3 | issn = 0036-8075 | pmid = 16825536 | journal = Science | bibcode=2006Sci...313..940W| doi-access = free | hdl = 10669/29855 | hdl-access = free }}

{{Main|Hail|List of costly or deadly hailstorms}}

File:Hagelkorn mit Anlagerungsschichten.jpg

Any form of thunderstorm that produces precipitating hailstones is known as a hailstorm.{{cite web |url=http://amsglossary.allenpress.com/glossary/search?p=1&query=Hailstorm |title=AMS Glossary |publisher=Amsglossary.allenpress.com |access-date=5 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20110606103908/http://amsglossary.allenpress.com/glossary/search?p=1&query=Hailstorm |archive-date=6 June 2011 }} Hailstorms are generally capable of developing in any geographic area where thunderclouds (cumulonimbus) are present, although they are most frequent in tropical and monsoon regions.{{cite web |url=http://www.buzzle.com/articles/facts-about-hailstorms.html |title=Facts about Hailstorms |publisher=Buzzle.com |date=13 July 2009 |access-date=5 December 2009 |archive-date=9 August 2009 |archive-url=https://web.archive.org/web/20090809185805/http://www.buzzle.com/articles/facts-about-hailstorms.html |url-status=usurped }} The updrafts and downdrafts within cumulonimbus clouds cause water molecules to freeze and solidify, creating hailstones and other forms of solid precipitation.{{cite web|url=http://www.andthensome.com/weather/hail.htm |title=Hailstorms |publisher=Andthensome.com |access-date=5 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090312094655/http://www.andthensome.com/weather/hail.htm |archive-date=12 March 2009 }} Due to their larger density, these hailstones become heavy enough to overcome the density of the cloud and fall towards the ground. The downdrafts in cumulonimbus clouds can also cause increases in the speed of the falling hailstones. The term hailstorm is usually used to describe the existence of significant quantities or size of hailstones.

Hailstones can cause serious damage, notably to automobiles, aircraft, skylights, glass-roofed structures, livestock, and crops.{{cite journal|url=http://www.cocorahs.org/media/docs/hail_1994.pdf|title=Hail, Hail, Hail ! The Summertime Hazard of Eastern Colorado|author=Nolan J. Doesken|journal=Colorado Climate|volume=17|issue=7|date=April 1994|access-date=18 July 2009|archive-date=25 November 2010|archive-url=https://web.archive.org/web/20101125163951/http://cocorahs.org/media/docs/hail_1994.pdf|url-status=dead}} Rarely, massive hailstones have been known to cause concussions or fatal head trauma. Hailstorms have been the cause of costly and deadly events throughout history. One of the earliest recorded incidents occurred around the 12th century in Wellesbourne, Britain.{{cite web |url=http://www.torro.org.uk/site/hail_extremes.php |title=Hailstorms: Extremes |publisher=TORRO |access-date=5 December 2009 |archive-date=21 February 2010 |archive-url=https://web.archive.org/web/20100221143125/http://www.torro.org.uk/site/hail_extremes.php |url-status=dead }} The largest hailstone in terms of maximum circumference and length ever recorded in the United States fell in 2003 in Aurora, Nebraska, USA. The hailstone had a diameter of 7 inches (18 cm) and a circumference of 18.75 inches (47.6 cm).Knight, C.A., and N.C. Knight, 2005: Very Large Hailstones From Aurora, Nebraska. Bull. Amer. Meteor. Soc., 86, 1773–1781.

{{clear}}

File:Kings Christian Church carpark Flooded.jpg

{{Main|Rain|Flood|Flash flood}}

Heavy rainfall can lead to a number of hazards, most of which are floods or hazards resulting from floods. Flooding is the inundation of areas that are not normally under water. It is typically divided into three classes: River flooding, which relates to rivers rising outside their normal banks; flash flooding, which is the process where a landscape, often in urban and arid environments, is subjected to rapid floods;{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=Flash+flood|title=Flash Flood|year=2009|access-date=9 September 2009|url-status=dead|archive-url=https://web.archive.org/web/20110606085246/http://amsglossary.allenpress.com/glossary/search?p=1&query=Flash+flood|archive-date=6 June 2011}} and coastal flooding, which can be caused by strong winds from tropical or non-tropical cyclones.{{cite web |url=http://www.noaawatch.gov/themes/coastal_inundation.php |title=Coastal Inundation: NOAA Watch: NOAA's All-Hazard Monitor: National Oceanic and Atmospheric Administration: U.S. Department of Commerce |publisher=Noaawatch.gov |date=1 May 2006 |access-date=20 November 2013 |url-status=dead |archive-url=https://web.archive.org/web/20131105140621/http://www.noaawatch.gov/themes/coastal_inundation.php |archive-date=5 November 2013 }} Meteorologically, excessive rains occur within a plume of air with high amounts of moisture (also known as an atmospheric river), which is directed around an upper level cold-core low or a tropical cyclone.{{cite conference|url=http://ams.confex.com/ams/90annual/techprogram/paper_161861.htm|title=An Analysis of Heavy Rainfall Weather Systems over Louisiana|date=20 January 2010|author1=Boniface J. Mills|author2=K. Falk|author3=J. Hansford|author4=B. Richardson|name-list-style=amp|conference=24th Conference of Hydrology|access-date=4 June 2010|archive-date=9 June 2011|archive-url=https://web.archive.org/web/20110609161717/http://ams.confex.com/ams/90annual/techprogram/paper_161861.htm|url-status=live}}

Flash flooding can frequently occur in slow-moving thunderstorms and are usually caused by the heavy liquid precipitation that accompanies it. Flash floods are most common in densely populated urban environments, where less plants and bodies of water are presented to absorb and contain the extra water. Flash flooding can be hazardous to small infrastructure, such as bridges, and weakly constructed buildings. Plants and crops in agricultural areas can be destroyed and devastated by the force of raging water. Automobiles parked within experiencing areas can also be displaced. Soil erosion can occur as well, exposing risks of landslide phenomena. Like all forms of flooding phenomenon, flash flooding can also spread and produce waterborne and insect-borne diseases cause by microorganisms. Flash flooding can be caused by extensive rainfall released by tropical cyclones of any strength or the sudden thawing effect of ice dams.{{cite web|url=http://weathereye.kgan.com/cadet/flood/about.html |title=Flash Flood! |author=WeatherEye |year=2007 |publisher=Sinclair Acquisition IV, Inc. |access-date=9 September 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090227073206/http://weathereye.kgan.com/cadet/flood/about.html |archive-date=27 February 2009 }}{{cite web|url=https://www.weather.gov/mrx/flood_and_flash|title=Definitions of flood and flash flood|author=National Weather Service Forecast Office Morristown, Tennessee|publisher=National Weather Service Southern Region Headquarters|date=7 March 2006|access-date=9 September 2009|archive-date=10 July 2017|archive-url=https://web.archive.org/web/20170710081202/http://www.weather.gov/mrx/flood_and_flash|url-status=live}}

{{Main|Monsoon}}

Seasonal wind shifts lead to long-lasting wet seasons, which produce the bulk of annual precipitation in areas such as Southeast Asia, Australia, Western Africa, eastern South America, Mexico, and the Philippines. Widespread flooding occurs if rainfall is excessive,{{cite web |title=Warden Message: Guyana Rainy Season Flood Hazards |url=https://www.osac.gov/Content/Report/94452980-440d-4816-b86a-15f4ace5a56c |publisher=Overseas Security Advisory Council |date=5 January 2009 |archive-url=https://web.archive.org/web/20200520224758/https://www.osac.gov/Content/Report/94452980-440d-4816-b86a-15f4ace5a56c |archive-date=20 May 2020 |url-status=live |access-date=5 February 2009}} which can lead to landslides and mudflows in mountainous areas.National Flood Insurance Program (2009). [http://www.floodsmart.gov/floodsmart/pages/media_resources/fact_calirain.jsp California's Rainy Season.] {{Webarchive|url=https://web.archive.org/web/20120301035439/http://www.floodsmart.gov/floodsmart/pages/media_resources/fact_calirain.jsp |date=1 March 2012 }} U.S. Federal Emergency Management Agency (FEMA). Retrieved on 5 February 2009. Floods cause rivers to exceed their capacity with nearby buildings becoming submerged.AFP (2009). [http://www.abc.net.au/news/stories/2009/01/12/2464296.htm Bali Hit By Wet Season Floods.] {{Webarchive|url=https://web.archive.org/web/20121108175818/http://www.abc.net.au/news/2009-01-12/bali-hit-by-wet-season-floods/263990 |date=8 November 2012 }} ABC News. Retrieved on 6 February 2009. Flooding may be exacerbated if there are fires during the previous dry season. This may cause soils that are sandy or composed of loam to become hydrophobic and repel water.Jack Ainsworth & Troy Alan Doss. [http://www.coastal.ca.gov/fire/ucsbfire.html Natural History of Fire & Flood Cycles.] {{Webarchive|url=https://web.archive.org/web/20120310063123/http://www.coastal.ca.gov/fire/ucsbfire.html |date=10 March 2012 }} California Coastal Commission. Retrieved on 5 February 2009.

Government organizations help their residents deal with wet-season floods though floodplain mapping and information on erosion control. Mapping is conducted to help determine areas that may be more prone to flooding.FESA (2007). [http://www.fesa.wa.gov.au/internet/upload/716567526/docs/flood.pdf Flood.] {{webarchive|url=https://web.archive.org/web/20090531073015/http://www.fesa.wa.gov.au/internet/upload/716567526/docs/flood.pdf |date=31 May 2009 }} Government of Western Australia. Retrieved on 6 February 2009. Erosion control instructions are provided through outreach over the telephone or the internet.King County Department of Development and Environmental Services (2009). [http://www.kingcounty.gov/property/permits/info/SpecialInterest/ConstructionIndustry/ErosionControl.aspx Erosion and Sediment Control for Construction Sites.] {{Webarchive|url=https://web.archive.org/web/20120513095553/http://kingcounty.gov/property/permits/info/SpecialInterest/ConstructionIndustry/ErosionControl.aspx |date=13 May 2012 }} King County, Washington Government. Retrieved on 6 February 2009.

Flood waters that occur during monsoon seasons can often host numerous protozoa, bacterial, and viral microorganisms.{{cite web |url=http://www.fairfaxcounty.gov/hd/alert/emerg/emerdisease.htm |title=Preventing Disease and Injury in a Flood – Fairfax County, Virginia |publisher=Fairfaxcounty.gov |access-date=5 December 2009 |archive-date=8 October 2009 |archive-url=https://web.archive.org/web/20091008055634/http://www.fairfaxcounty.gov/hd/alert/emerg/emerdisease.htm |url-status=live }} Mosquitoes and flies will lay their eggs within the contaminated bodies of water. These disease agents may cause infections of foodborne and waterborne diseases. Diseases associated with exposure to flood waters include malaria, cholera, typhoid, hepatitis A, and the common cold.{{cite web |url=http://www.zeenews.com/news548974.html |title=Monsoon diseases: Prevention and cure |publisher=Zeenews.com |date=21 July 2009 |access-date=5 December 2009 |archive-date=18 November 2009 |archive-url=https://web.archive.org/web/20091118173928/http://www.zeenews.com/news548974.html |url-status=live }} Possible trench foot infections may also occur when personnel are exposed for extended periods of time within flooded areas.{{Cite web|url=http://ww38.australianetwork.com/news/stories/asiapacific_stories_2376322.htm|title=australianetwork.com|website=ww38.australianetwork.com|access-date=30 October 2023|archive-date=29 April 2023|archive-url=https://web.archive.org/web/20230429161644/http://ww38.australianetwork.com/news/stories/asiapacific_stories_2376322.htm|url-status=live}}

{{Main|Tropical cyclone}}

File:Hurricane andrew fema 2563.jpg is a good example of the damage caused by a category 5 Tropical cyclone]]

A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain or squalls. A tropical cyclone feeds on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. Tropical cyclones may produce torrential rain, high waves, and damaging storm surge.{{cite journal|author=James M. Shultz, Jill Russell and Zelde Espinel|year=2005|title=Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development|journal=Epidemiologic Reviews|volume=27|pages=21–35|doi=10.1093/epirev/mxi011|pmid=15958424|doi-access=free}} Heavy rains produce significant inland flooding. Storm surges may produce extensive coastal flooding up to {{convert|40|km|mi}} from the coastline.

Although cyclones take an enormous toll in lives and personal property, they are also important factors in the precipitation regimes of areas they affect. They bring much-needed precipitation to otherwise dry regions.{{cite web|year=2005|url=http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html|title=2005 Tropical Eastern North Pacific Hurricane Outlook|publisher=National Oceanic and Atmospheric Administration|access-date=2 May 2006|archive-date=14 June 2009|archive-url=https://web.archive.org/web/20090614024616/http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html|url-status=live}} Areas in their path can receive a year's worth of rainfall from a tropical cyclone passage.{{cite news|author=Jack Williams|url=https://www.usatoday.com/weather/whhcalif.htm|title=Background: California's tropical storms|work=USA Today|access-date=7 February 2009|date=17 May 2005|archive-date=26 February 2009|archive-url=https://web.archive.org/web/20090226172558/http://www.usatoday.com/weather/whhcalif.htm|url-status=live}} Tropical cyclones can also relieve drought conditions.National Oceanic and Atmospheric Administration. [http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html 2005 Tropical Eastern North Pacific Hurricane Outlook.] {{Webarchive|url=https://web.archive.org/web/20090614024616/http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html |date=14 June 2009 }} Retrieved on 2 May 2006. They also carry heat and energy away from the tropics and transport it toward temperate latitudes, which makes them an important part of the global atmospheric circulation mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere.

{{Main|Blizzard|Lake-effect snow|Snow|Winter storm}}

File:Buffalo snow storm3.jpg in October 2006]]

When extratropical cyclones deposit heavy, wet snow with a snow-water equivalent (SWE) ratio of between 6:1 and 12:1 and a weight in excess of 10 pounds per square foot (~50 kg/m²){{cite web

|url=http://www.weather.com/blog/weather/8_10843.html

|title=Historic snowfall for the Niagara Frontier

|author=Stu Ostro

|publisher=Weather Channel blog

|date=12 October 2006

|access-date=7 July 2009

|url-status=dead

|archive-url=https://web.archive.org/web/20091020071219/http://www.weather.com/blog/weather/8_10843.html

|archive-date=20 October 2009

}} piles onto trees or electricity lines, significant damage may occur on a scale usually associated with strong tropical cyclones.{{cite web|url=http://www.erh.noaa.gov/buf/storm101206.html|title=Historic Lake Effect Snow Storm of October 12–13, 2006|publisher=National Weather Service Forecast Office in Buffalo, New York|date=21 October 2006|access-date=8 July 2009|archive-date=16 October 2015|archive-url=https://web.archive.org/web/20151016013049/http://www.erh.noaa.gov/buf/storm101206.html|url-status=live}} An avalanche can occur with a sudden thermal or mechanical impact on snow that has accumulated on a mountain, which causes the snow to rush downhill suddenly. Preceding an avalanche is a phenomenon known as an avalanche wind caused by the approaching avalanche itself, which adds to its destructive potential.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=avalanche&submit=Search|title=Avalanche| publisher=American Meteorological Society|year=2009|access-date=30 June 2009|archive-url=https://web.archive.org/web/20110606085517/http://amsglossary.allenpress.com/glossary/search?p=1&query=avalanche&submit=Search|archive-date=6 June 2011|url-status=dead}} Large amounts of snow that accumulate on top of man-made structures can lead to structural failure.{{cite news |author=Gershon Fishbein |title=A Winter's Tale of Tragedy |url=https://www.washingtonpost.com/wp-dyn/content/article/2009/01/21/AR2009012101298.html |newspaper=Washington Post |date=22 January 2009 |access-date=24 January 2009 |archive-date=4 June 2011 |archive-url=https://web.archive.org/web/20110604153214/http://www.washingtonpost.com/wp-dyn/content/article/2009/01/21/AR2009012101298.html |url-status=live }} During snowmelt, acidic precipitation that previously fell in the snow pack is released and harms marine life.{{cite journal|url=http://www.avalanche.org/moonstone/TAR/avi%20review%20articles/Of%20Wet%20Snow,%20Slush%20&%20Snowballs.htm |archive-url=https://web.archive.org/web/20150909153808/http://www.avalanche.org/moonstone/TAR/avi%20review%20articles/Of%20Wet%20Snow%2C%20Slush%20%26%20Snowballs.htm |url-status=dead |archive-date=9 September 2015 |title=Of Wet Snow, Slush, and Snow Balls |access-date=12 July 2009 |date=March 1995 |volume=13 |issue=5 |journal=The Avalanche Review |author=Samuel C. Colbeck }}

Lake-effect snow is produced in the winter in the shape of one or more elongated bands. This occurs when cold winds move across long expanses of warmer lake water, providing energy and picking up water vapor, which then freezes and is deposited on the lee shores.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=lake-effect+snow&submit=Search|title=Lake-effect snow|access-date=15 June 2009|year=2009|publisher=American Meteorological Society|archive-url=https://web.archive.org/web/20110606103629/http://amsglossary.allenpress.com/glossary/search?p=1&query=lake-effect+snow&submit=Search|archive-date=6 June 2011|url-status=dead}} For more information on this effect see the main article.

Conditions within blizzards often include large quantities of blowing snow and strong winds that may significantly reduce visibility. Reduced viability of personnel on foot may result in extended exposure to the blizzard and increase the chance of becoming lost. The strong winds associated with blizzards create wind chill that can result in frostbites and hypothermia. The strong winds present in blizzards are capable of damaging plants and may cause power outages, frozen pipes, and cut off fuel lines.{{cite web |url=http://www.ussartf.org/blizzards.htm |title=Blizzards |publisher=Ussartf.org |access-date=5 December 2009 |archive-date=9 March 2010 |archive-url=https://web.archive.org/web/20100309060604/http://www.ussartf.org/blizzards.htm |url-status=live }}

{{Main|Ice storm}}

File:20081214-shrewsbury-ice-storm-damage-looking-south-2.jpg

Ice storms are also known as a Silver storm, referring to the color of the freezing precipitation. Ice storms are caused by liquid precipitation which freezes upon cold surfaces and leads to the gradual development of a thickening layer of ice.{{cite web |url=http://amsglossary.allenpress.com/glossary/search?p=1&query=Ice+storm |title=AMS Glossary |publisher=Amsglossary.allenpress.com |access-date=5 December 2009 |archive-url=https://web.archive.org/web/20110606153248/http://amsglossary.allenpress.com/glossary/search?p=1&query=Ice+storm |archive-date=6 June 2011 |url-status=dead }}

The accumulations of ice during the storm can be extremely destructive. Trees and vegetation can be destroyed and in turn may bring down power lines, causing the loss of heat and communication lines.{{cite web |url=http://www.weather.gov/glossary/index.php?word=ice+storm |title=Glossary – NOAA's National Weather Service |publisher=Weather.gov |date=25 June 2009 |access-date=5 December 2009 |archive-date=20 March 2012 |archive-url=https://web.archive.org/web/20120320054142/http://www.weather.gov/glossary/index.php?word=ice+storm |url-status=live }} Roofs of buildings and automobiles may be severely damaged. Gas pipes can become frozen or even damaged causing gas leaks. Avalanches may develop due to the extra weight of the ice present. Visibility can be reduced dramatically. The aftermath of an ice storm may result in severe flooding due to sudden thawing, with large quantities of displaced water, especially near lakes, rivers, and bodies of water.{{cite web|url=http://www.nws.noaa.gov/om/winterstorm/winterstorms.pdf |title=WinterStorms.p65 |access-date=5 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090825020946/http://www.nws.noaa.gov/om/winterstorm/winterstorms.pdf |archive-date=25 August 2009 }}

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{{Main|Drought}}

File:Fields outside benambra.jpg

Another form of severe weather is drought, which is a prolonged period of persistently dry weather (that is, absence of precipitation).{{cite web|last=NOAA Forecast Office, Flagstaff, Arizona|title=What is Meant by the Term Drought?|url=http://www.wrh.noaa.gov/fgz/science/drought.php?wfo=fgz|access-date=29 March 2012|archive-date=23 July 2011|archive-url=https://web.archive.org/web/20110723004053/http://www.wrh.noaa.gov/fgz/science/drought.php?wfo=fgz|url-status=live}} Although droughts do not develop or progress as quickly as other forms of severe weather,{{cite web|last=Earth Observatory|title=Drought: The Creeping Disaster|url=http://earthobservatory.nasa.gov/Features/DroughtFacts/|access-date=29 March 2012|date=28 August 2000|archive-date=19 January 2012|archive-url=https://web.archive.org/web/20120119155704/http://earthobservatory.nasa.gov/Features/DroughtFacts/|url-status=live}} their effects can be just as deadly; in fact, droughts are classified and measured based upon these effects. Droughts have a variety of severe effects; they can cause crops to fail, and they can severely deplete water resources, sometimes interfering with human life. A drought in the 1930s known as the Dust Bowl affected 50 million acres of farmland in the central United States. In economic terms, they can cost many billions of dollars: a drought in the United States in 1988 caused over $40 billion in losses,{{cite web|url=https://www.ncdc.noaa.gov/billions/events|title=Billion-Dollar Weather and Climate Disasters: Table of Events | National Centers for Environmental Information (NCEI)|website=www.ncdc.noaa.gov|access-date=26 December 2019|archive-date=25 December 2012|archive-url=https://web.archive.org/web/20121225015735/http://www.ncdc.noaa.gov/billions/events|url-status=live}} exceeding the economic totals of Hurricane Andrew, the Great Flood of 1993, and the 1989 Loma Prieta earthquake. In addition to the other severe effects, the dry conditions caused by droughts also significantly increase the risk of wildfires.

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{{Main|Heat wave}}

{{See also|Heat index}}

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Although official definitions vary, a heat wave is generally defined as a prolonged period with excessive heat.{{cite web|url=http://www.ga.gov.au/servlet/BigObjFileManager?bigobjid=GA6525|title=Meteorological hazards|publisher=Geoscience Australia|work=Natural hazard risk in Perth, Western Australia – Cities Project Perth Report|first1=Joe|last1=Courtney|first2=Miriam|last2=Middelmann|format=PDF|year=2005|access-date=25 December 2012|archive-date=28 July 2020|archive-url=https://web.archive.org/web/20200728084506/http://www.ga.gov.au/webtemp/image_cache/GA6525.pdf|url-status=live}} Although heat waves do not cause as much economic damage as other types of severe weather, they are extremely dangerous to humans and animals: according to the United States National Weather Service, the average total number of heat-related fatalities each year is higher than the combined total fatalities for floods, tornadoes, lightning strikes, and hurricanes.{{cite web|last=Office of Climate, Water, and Weather Services, NOAA|title=Heat:A Major Killer|url=http://www.nws.noaa.gov/om/heat/index.shtml|access-date=30 March 2012|archive-date=29 May 2012|archive-url=https://web.archive.org/web/20120529094057/http://www.nws.noaa.gov/om/heat/index.shtml|url-status=live}} In Australia, heat waves cause more fatalities than any other type of severe weather. The dry conditions that may accompany heat waves can also severely affect plant life as the plants lose moisture and die.{{cite web|last=Australian Government Attorney-General's Department |title=Heatwaves: Get the Facts |url=http://www.em.gov.au/sites/schools/Getthefacts/Heatwaves/Pages/default.aspx |access-date=30 March 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120317011535/http://www.em.gov.au/sites/schools/Getthefacts/Heatwaves/Pages/default.aspx |archive-date=17 March 2012 }} Heat waves are often more severe when combined with high humidity.

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• List of natural disasters by death toll
• List of severe weather phenomena
• Storm chasing

{{Reflist|30em}}

• [https://www.bchousing.org/publications/MBAR-Severe-Storms.pdf Design Discussion Primer – Severe Storms] residential building design strategies.
• {{cite report |first1=Ben |last1=Clarke |first2=Friederike |last2=Otto |url=https://www.worldweatherattribution.org/wp-content/uploads/ENG_WWA-Reporting-extreme-weather-and-climate-change.pdf |title=Reporting extreme weather and climate change: A guide for journalists |publisher=World Weather Attribution |year=2022}}

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{{DEFAULTSORT:Severe Weather}}

Category:Weather hazards