Numerical Weather Prediction

An animated image of NAM simulated radar reflectivities, forecast from 00UTC on July 10, 2012 to July 13, 2012 at 12UTC—a three and a half day forecast—in three hourly intervals. In the initial few frames, hurricane Emilia can be seen in the bottom left corner spinning off to the west. This image was produced with the Grid Analysis and Display System (GrADS) and ImageMagick.

The form of model data we are most familiar with on a day-to-day basis comes from Numerical Weather Prediction (NWP). NWP is focused on taking current observations of weather and processing these data with computer models to forecast the future state of weather. Knowing the current state of the weather is just as important as the numerical computer models processing the data. Current weather observations are input to the numerical computer models through a process known as data assimilation to produce output of temperature, precipitation, and hundreds of other meteorological elements from the oceans to the top of the atmosphere.

The following numerical weather prediction data, and data assimilation data (input observational weather data), are available through NOMADS.

• Global Data Assimilation System (GDAS)
  GDAS is the set of assimilation data, both input and output, in various formats, for the Global Forecast System model, which has been archived since 2004.
• Global Ensemble Forecast System (GEFS)
  GEFS is a global-coverage weather forecast model made up of 21 separate forecasts, or ensemble members, used to quantify the amount of uncertainty in a forecast. GEFS is produced four times a day with weather forecasts going out to 16 days.
• Global Forecast System (GFS)
  The GFS model is a coupled weather forecast model, composed of four separate models which work together to provide an accurate picture of weather conditions. The entire globe is covered by the GFS down to a horizontal resolution of 28km.
• North American Model (NAM)
  NAM is a regional weather forecast model covering North America down to a horizontal resolution of 12km. Dozens of weather parameters are available from the NAM grids, from temperature and precipitation to lightning and turbulent kinetic energy.
• Rapid Refresh (RAP)
  RAP is a regional weather forecast model of North America, with separate subgrids (with different horizontal resolutions) within the overall North America domain. RAP forecasts are generated every hour with forecast lengths going out 18 hours.
• Rapid Update Cycle (RUC)
  RUC is a regional weather forecast model of the Continental United States (CONUS) with forecast lengths going out 12 hours. RUC data are no longer produced operationally by the National Centers for Environmental Prediction (NCEP).