prognostic chart

The forecast map showing the state of the atmosphere at a future time is called a prognostic chart. Prognostic charts generated by computer models are sometimes referred to as machine-made forecasts.{{cite book|url=https://books.google.com/books?id=2Yn29IFukbgC&pg=PA244|page=244|author=Ahrens, C. Donald|title=Essentials of meteorology: an invitation to the atmosphere|year=2008|publisher=Cengage Learning|isbn=978-0-495-11558-8}}

Surface weather prognostic charts for mariners indicate the positions of high and low pressure areas, as well as frontal zones, up to five days into the future. Surface wind direction and speed is also forecast on this type of chart. Wave prognostic charts show the expected sea state at some future time.{{cite book|url=https://books.google.com/books?id=rlwuk6W-Uz4C&pg=PA236|title=Weather For th Mariner|author=Kotsch, William J.|pages=236–239|publisher=Naval Institute Press|year=1983|isbn=978-0-87021-756-2}} Low-level prognostic charts used by aviators show the forecast between the Earth's surface and {{convert|24000|ft|m}} above sea level over the next two days. They show areas where visual flight rules are in effect, instrument flight rules are in effect, the height of the freezing level, the location of weather features, and areas of moderate to severe turbulence.{{cite book|url=https://www.cnatra.navy.mil/pubs/folder5/T34C/P-304.pdf|archive-url=https://web.archive.org/web/20110722192332/https://www.cnatra.navy.mil/pubs/folder5/T34C/P-304.pdf|url-status=dead|archive-date=July 22, 2011|title=Aviation Weather Student Guide|author=United States Naval Air Training Command|publisher=Corpus Christi, Texas Naval Air Station|pages=2-5,2-6|date=April 2003|accessdate=2011-02-26}} Prognostic charts can be made of isentropic surfaces (along a certain potential temperature surface determined in kelvins) in regards to moisture advection, mean temperatures at the surface, mean sea level pressures, and precipitation either for a single day or multiple days.{{cite book|url=https://books.google.com/books?id=Jd5pc6VfWxwC&pg=PA646|pages=647–651|title=Climate and Man: Part Two|author=United States Department of Agriculture|author-link=United States Department of Agriculture|year=1941|isbn=978-1-4102-1539-0|publisher=The Minerva Group, Inc.}} For purposes of severe weather, prognostic charts can be issued to depict current weather watches, convective outlooks for thunderstorms multiple days into the future, and fire weather outlooks.

{{See also|Weather forecasting}}

File:manualfcst36hrs.gif

Manual prognostic charts depict tropical cyclones, turbulence, weather fronts, rain and snow areas, precipitation type and coverage indicators, as well as centers of high and low pressure.{{cite book|pages=9-30, 9-31|title=Gliding Flyer Handbook|author=Federal Aviation Administration|author-link=Federal Aviation Administration|year=2007|publisher=Skyhorse Publishing, Inc.|isbn=978-1-60239-061-4|url=https://books.google.com/books?id=y1CCxCYbXEMC&pg=SA9-PA31}} Within the United States, these types of maps are generated by the Hydrometeorological Prediction Center,{{cite web|url=http://www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php|title=Short Range Forecasts|author=Hydrometeorological Prediction Center|author-link=Hydrometeorological Prediction Center|publisher=National Centers for Environmental Prediction|year=2011|accessdate=2011-02-26}} the Storm Prediction Center,{{cite web|url=http://www.spc.ncep.noaa.gov/products/|title=Forecast Products|author=Storm Prediction Center|author-link=Storm Prediction Center|publisher=National Centers for Environmental Prediction|year=2011|accessdate=2011-02-27}} the Ocean Prediction Center,{{citation|author=Ocean Prediction Center|author-link=Ocean Prediction Center|title=Atlantic Offshore|publisher=National Centers for Environmental Prediction|year=2011}} and the National Hurricane Center. The Aviation Weather Center re-sends these maps, and also generates specialized maps for aviation.{{cite web|url=http://aviationweather.gov/adds/progs/|title=Analysis and forecast surface conditions (prog charts)|author=Aviation Weather Center|author-link=Aviation Weather Center|publisher=National Centers for Environmental Prediction|year=2011|accessdate=2011-02-26}}

{{Main|Atmospheric model}}

File:GFS 850 MB.PNG geopotential height and temperature from the Global Forecast System|alt=A prognostic chart of the North American continent provides geopotential heights, temperatures, and wind velocities at regular intervals. The values are taken at the altitude corresponding to the 850-millibar pressure surface.]]

Atmospheric models are computer programs that produce meteorological information, including prognostic charts, for future times at given locations and altitudes.{{cite book|author=Ahrens, C. Donald|page=244|isbn=978-0-495-11558-8|year=2008|publisher=Cengage Learning|title=Essentials of meteorology: an invitation to the atmosphere|url=https://books.google.com/books?id=2Yn29IFukbgC&pg=PA244}} Within any modern model is a set of equations, known as the primitive equations, used to predict the future state of the atmosphere.{{cite book|last=Pielke|first=Roger A.|title=Mesoscale Meteorological Modeling|url=https://archive.org/details/mesoscalemeteoro00srro|url-access=limited|year=2002|publisher=Academic Press|isbn=0-12-554766-8|pages=[https://archive.org/details/mesoscalemeteoro00srro/page/n64 48]–49}} These equations—along with the ideal gas law—are used to evolve the density, pressure, and potential temperature scalar fields and the velocity vector field of the atmosphere through time. Additional transport equations for pollutants and other aerosols are included in some primitive-equation mesoscale models as well.{{cite book|last=Pielke|first=Roger A.|title=Mesoscale Meteorological Modeling|url=https://archive.org/details/mesoscalemeteoro00srro|url-access=limited|year=2002|publisher=Academic Press|isbn=0-12-554766-8|pages=[https://archive.org/details/mesoscalemeteoro00srro/page/n34 18]–19}} These equations are initialized from the analysis data and rates of change are determined. These rates of change predict the state of the atmosphere a short time into the future; the time increment for this prediction is called a time step. This time stepping is repeated until the solution reaches the desired forecast time.{{cite book|last=Pielke|first=Roger A.|title=Mesoscale Meteorological Modeling|url=https://archive.org/details/mesoscalemeteoro00srro|url-access=limited|year=2002|publisher=Academic Press|isbn=0-12-554766-8|pages=[https://archive.org/details/mesoscalemeteoro00srro/page/n301 285]–287}} Time steps for global models are on the order of tens of minutes,{{cite book|url=https://books.google.com/books?id=JZikIbXzipwC&pg=PA131|page=132|author1=Sunderam, V. S. |author2=van Albada, G. Dick |author3=Peter, M. A. |author4=Sloot, J. J. Dongarra |title=Computational Science – ICCS 2005: 5th International Conference, Atlanta, GA, USA, May 22–25, 2005, Proceedings, Part 1|year=2005|publisher=Springer|isbn=978-3-540-26032-5}} while time steps for regional models are between one and four minutes.{{cite book|url=https://books.google.com/books?id=UV6PnF2z5_wC&pg=PA276|page=276|title=Developments in teracomputing: proceedings of the ninth ECMWF Workshop on the Use of High Performance Computing in Meteorology|author=Zwieflhofer, Walter|author2=Kreitz, Norbert|author3=European Centre for Medium Range Weather Forecasts|year=2001|publisher=World Scientific|isbn=978-981-02-4761-4}} The global models are run outwards to varying times into the future. The UKMET Unified Model is run six days into the future,{{cite book|pages=295–296|url=https://books.google.com/books?id=6gFiunmKWWAC&pg=PA297|title=Global Perspectives on Tropical Cyclones: From Science to Mitigation|author1=Chan, Johnny C. L. |author2=Jeffrey D. Kepert |name-list-style=amp |year=2010|publisher=World Scientific|isbn=978-981-4293-47-1}} the European Centre for Medium-Range Weather Forecasts model is run out to 10 days into the future,{{cite book|url=https://books.google.com/books?id=fhW5oDv3EPsC&pg=PA474|page=480|author=Holton, James R.|title=An introduction to dynamic meteorology, Volume 1|year=2004|publisher=Academic Press|isbn=978-0-12-354015-7}} while the Global Forecast System model run by the Environmental Modeling Center is run 16 days into the future.{{cite book|url=https://books.google.com/books?id=mTZvR3R6YdkC&pg=PA121|page=121|title=Famine early warning systems and remote sensing data|author=Brown, Molly E.|publisher=Springer|year=2008|isbn=978-3-540-75367-4}}

Around 1950, a good surface prognostic chart was considered to be one whose isobars were in the correct location.{{cite book|url=http://catdir.loc.gov/catdir/samples/cam033/2001052687.pdf|page=7|title=Atmospheric Modeling, Data Assimilation and Predictability|publisher=Cambridge University Press|author=Eugenia Kalnay|author-link=Eugenia Kalnay|isbn=0-521-79179-0|year=2003|accessdate=2011-02-27}} By 1957, it was proposed when isobars or height lines at the {{convert|500|hPa|inHg}} pressure level in the atmosphere were being verified, that the degree of persistence should be considered so as to avoid getting bad forecasts for slow moving systems too much credit.{{cite journal|page=314|title=A Note on Verification of Prognostic Charts|author=Sverre Petterssen|journal=Tellus A|year=1957|volume=9|issue=3|doi=10.1111/j.2153-3490.1957.tb01887.x|bibcode=1957Tell....9..313P }}

• Weather map

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Category:Weather forecasting