Explanation of Current NGM MOS

Since 1987, statistical guidance based on the Nested Grid Model (NGM) has been available to National Weather Service and private forecasters for use in the production of public and aviation forecasts. Since 1989, the guidance has been based on applying the Model Output Statistics (MOS) approach to output from the NGM. Forecasters generally view the NGM-based MOS guidance for stations in the contiguous U.S. through the FOUS14 alphanumeric message. In the NWS, this message is known as the FWC product because of the manner in which the bulletin is identified in AFOS. The guidance is available for 6- through 60-h forecast projections from both the 0000 and 1200 UTC runs of the NGM. While the FOUS14 message contains guidance for 565 sites in the contiguous U.S., another series of FOUS14-like bulletins, namely, the FOAK25-FOAK29 messages, contain NGM-based MOS guidance for 60 stations in Alaska. Finally, NGM MOS forecasts for over 130 military sites are provided to the U.S. Air Force Weather Agency through another series of alphanumeric messages. The guidance for some of these military bases is also available in the FOUS14 bulletin. In all cases, the messages are issued at approximately 0330 and 1530 UTC every day.

The NGM MOS alphanumeric guidance provides objective forecasts of the maximum/minimum temperature; the 2-m air temperature and dew point; wind speed and direction; categorical cloud, precipitation, and snowfall amounts; categorical precipitation type, ceiling height, visibility, and obstruction to vision; and the probability of precipitation, thunderstorms, severe weather, freezing precipitation, and snow. The latter three probabilities are conditional on thunderstorms (for severe weather) or precipitation (for freezing precipitation and snow) occurring. Further details on the bulletin may be found in the Green Card. Because the NGM MOS alphanumeric message does not display all the probabilities for all the possible stations available, a series of binary products (JSMT41-49) contain all of the MOS guidance in BUFR format. For additional details on the NGM MOS guidance, please consult the appropriate Technical Procedures Bulletins (TPB's) available from the Office of Meteorology.

While the NWS is planning a new package of MOS guidance based on the Aviation (AVN) run of the Global Spectral Model, NWS and private sector users have asked that a minimum of 1- year overlap be provided between the NGM MOS and the new AVN MOS guidance. Current plans call for the NGM MOS guidance to be available until approximately April 2001. See www.ncep.noaa.gov/NCO/PMB/announcements/ngmwkshp.html for additional details on the future of the NGM and NGM MOS.

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Last Updated August 4, 1999