Numerical weather prediction: Difference between revisions

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==Model output statistics==

{{Main|Model output statistics}}

Because forecast models based upon the equations for atmospheric dynamics do not perfectly determine weather conditions, statistical methods have been developed to attempt to correct the forecasts. Statistical models were created based upon the three-dimensional fields produced by numerical weather models, surface observations and the climatological conditions for specific locations. These statistical models are collectively referred to as [[model output statistics]] (MOS),<ref>{{cite book|url=https://books.google.com/books?id=blEMoIKX_0IC&pg=PA188|page=189|title=When nature strikes: weather disasters and the law|author=Baum, Marsha L.|publisher=Greenwood Publishing Group|year=2007|isbn=978-0-275-22129-4}}</ref> and were developed by the [[National Weather Service]] for their suite of weather forecasting models in the late 1960s.<ref name="MOS">{{cite book|title=Model output statistics forecast guidance|first=Harry | last=Hughes|publisher=United States Air Force Environmental Technical Applications Center|year=1976|pages=1–16|url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a037148.pdf|archive-url=https://web.archive.org/web/20190617044348/https://apps.dtic.mil/dtic/tr/fulltext/u2/a037148.pdf|url-status=deadlive|archive-date=June 17, 2019}}</ref><ref>{{cite journal|last=Glahn|first=Harry R.|author2=Lowry, Dale A. |title=The Use of Model Output Statistics (MOS) in Objective Weather Forecasting|journal=[[Journal of Applied Meteorology]]|date=December 1972|volume=11|issue=8|pages=1203–1211|doi=10.1175/1520-0450(1972)011<1203:TUOMOS>2.0.CO;2|bibcode=1972JApMe..11.1203G|doi-access=free}}</ref>

Model output statistics differ from the ''perfect prog'' technique, which assumes that the output of numerical weather prediction guidance is perfect.<ref>{{cite book|url=https://books.google.com/books?id=QwzHZ-wV-BAC&pg=PA1144|page=1144|title=Fog and boundary layer clouds: fog visibility and forecasting|author=Gultepe, Ismail|publisher=Springer|year=2007|isbn=978-3-7643-8418-0|access-date=2011-02-11}}</ref> MOS can correct for local effects that cannot be resolved by the model due to insufficient grid resolution, as well as model biases. Because MOS is run after its respective global or regional model, its production is known as post-processing. Forecast parameters within MOS include maximum and minimum temperatures, percentage chance of rain within a several hour period, precipitation amount expected, chance that the precipitation will be frozen in nature, chance for thunderstorms, cloudiness, and surface winds.<ref>{{cite book|url=https://books.google.com/books?id=Xs9LiGpNX-AC&pg=PA171|page=172|author1=Barry, Roger Graham |author2=Chorley, Richard J. |title=Atmosphere, weather, and climate|publisher=Psychology Press|year=2003|access-date=2011-02-11|isbn=978-0-415-27171-4}}</ref>