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Numerical weather prediction uses current weather conditions as input into mathematical models of the atmosphere to predict the weather. Manipulating the huge datasets and performing the complex calculations necessary to do this on a resolution fine enough to make the results useful requires the use of some of the most powerful supercomputers in the world. Use of model ensemble forecasts helps to define the forecast uncertainty and extend weather forecasting farther into the future than would otherwise be possible.

Operational numerical weather prediction (i.e., routine predictions for practical use) began in 1955 under a joint project by the U.S. Air Force, Navy, and Weather Bureau.

The forecasts are computed using mathematical equations for the physics and dynamics of the atmosphere. These equations are nonlinear and are impossible to solve exactly. Therefore, numerical methods obtain approximate solutions. Different models use different solution methods. Global models often use spectral methods for the horizontal dimensions and finite difference methods for the vertical dimension, while regional models usually use finite-difference methods in all three dimensions. Regional models also can use finer grids to explicitly resolve smaller-scale meteorological phenomena, since they do not have to solve equations for the whole globe.

Models are initialized using observed data from radiosondes, weather satellites, and surface weather observations. The irregularly-spaced observations are processed by data assimilation and objective analysis methods, which perform quality control and obtain values at locations usable by the model's mathematical algorithms (usually an evenly-spaced grid). The data are then used in the model as the starting point for a forecast. Commonly, the set of equations used is known as the primitive equations. These equations are initialized from the analysis data and rates of change are determined. The rates of change predict the state of the atmosphere a short time into the future. The equations are then applied to this new atmospheric state to find new rates of change, and these new rates of change predict the atmosphere at a yet further time into the future. This time stepping procedure is continually repeated until the solution reaches the desired forecast time. The length of the time step is related to the distance between the points on the computational grid. Time steps for global climate models may be on the order of tens of minutes, while time steps for regional models may be a few seconds to a few minutes.

- GFS - Global Forecast System (previously AVN) - developed by NOAA
- NOGAPS - developed by the US Navy to compare with the GFS
- GEM Global Environmental Multiscale Model - developed by the Meteorological Service of Canada (MSC)
- IFS developed by the European Centre for Medium-Range Weather Forecasts
- UM - Unified Model developed by the UK Met Office, but is hand-corrected by professional forecasters
- GME - developed by the German Weather Service, DWD, NWP Global model of DWD
- ARPEGE - developed by the French Weather Service, Météo France
- IGCM - Intermediate General Circulation Model - developed by members of the Department of Meteorology at the University of Reading

- WRF The Weather Research and Forecasting Model was developed cooperatively by NCEP and the meteorological research community. WRF has several configurations, including:

- * WRF-NMM The WRF Nonhydrostatic Mesoscale Model is the primary short-term weather forecast model for the U.S., replacing the Eta model.

- * AR-WRF Advanced Research WRF developed primarily at the U.S. National Center for Atmospheric Research (NCAR)

- NAM The term North American Mesoscale model refers to whatever regional model NCEP operates over the North American domain. NCEP began using this designation system in January 2005. Between January 2005 and May 2006 the Eta model (began in Yugoslavia (now Serbia) during the 1970s by Zaviša Janjić and Fedor Mesinger) used this designation. Beginning in May 2006, NCEP began to use the WRF-NMM as the operational NAM.
- RAMS the Regional Atmospheric Modeling System developed at Colorado State University for numerical simulations of atmospheric meteorology and other environmental phenomena on scales from meters to 100's of kilometers - now supported in the public domain.
- MM5 the Fifth Generation Penn State/NCAR Mesoscale Model
- ARPS the Advanced Region Prediction System developed at the University of Oklahoma is a comprehensive multi-scale nonhydrostatic simulation and prediction system that can be used for regional-scale weather prediction up to the tornado-scale simulation and prediction. Advanced radar data assimilation for thunderstorm prediction is a key part of the system.
- HIRLAM High Resolution Limited Area Model
- GEM-LAM Global Environmental Multiscale Limited Area Model, the high resolution (2.5 km) GEM by the Meteorological Service of Canada (MSC)
- ALADIN The high-resolution limited-area hydrostatic and non-hydrostatic model developed and operated by several European and North African countries under the leadership of Météo-France
- COSMO The COSMO Model, formerly known as LM, Lokal-Modell, aLMo or LAMI, is a limited-area non hydrostatic model developed within the framework of the Consortium for Small-Scale Modeling (Germany, Switzerland, Italy, Poland, Greece, and Romania).

- Tropical cyclone forecast model
- Atmospheric physics
- Atmospheric thermodynamics
- Frederick Gale Shuman

- Beniston, Martin. From Turbulence to Climate: Numerical Investigations of the Atmosphere with a Hierarchy of Models. Berlin: Springer, 1998.
- Kalnay, Eugenia. Atmospheric Modeling, Data Assimilation and Predictability. Cambridge University Press, 2003.
- Thompson, Philip. Numerical Weather Analysis and Prediction. New York: The Macmillan Company, 1961.
- Pielke, Roger A. Mesoscale Meteorological Modeling. Orlando: Academic Press, Inc., 1984.
- U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service. National Weather Service Handbook No. 1 - Facsimile Products. Washington, DC: Department of Commerce, 1979.

- Description of models used in the United States circa 1995
- meteoblue - free maps and diagrams of NWP (high resolution NMM and GFS) data worldwide
- NOAA Supercomputers
- Wetterzentrale (German only) - nearly all NWP data available plotted on charts
- Air Resources Laboratory
- Fleet Numerical Meteorology and Oceanography Center
- European Centre for Medium-Range Weather Forecasts
- University of Reading Department of Meteorology
- WRF Source Codes and Graphics Software Download Page
- RAMS source code available under the GNU public license
- MM5 Source Code download
- The source code of ARPS
- ALADIN Community web pages

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Last updated on Wednesday September 24, 2008 at 05:15:00 PDT (GMT -0700)

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This article is licensed under the GNU Free Documentation License.

Last updated on Wednesday September 24, 2008 at 05:15:00 PDT (GMT -0700)

View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation

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