Changes to the MOS Products Based on NCEP's Global Forecast System (GFS) Effective December 16, 2003

Effective with the 1200 UTC forecast cycle on December 16, 2003, MDL will be making a series of changes to the MOS products based on NCEP's GFS model. These changes include unifying the AVN and MRF MOS into one GFS MOS system, changing the stations for which guidance is available, adding snowfall amount guidance to the text products, implementing new prediction equations for several elements, and changing the experimental ensemble MOS. All of these changes are outlined below.

I. Unified GFS MOS

When the new AVN and MRF MOS were first developed in 2000, NCEP was running two separate configurations of the global forecast model -- the Aviation run (AVN), and the medium-range forecast run (MRF). MDL maintained separate model archives for each run, and developed separate MOS forecast equations. On December 16th, MDL will unify our AVN and MRF MOS systems into one GFS MOS system that generates short-range (MAV) and extended-range (MEX) products. We will still continue to produce the same alphanumeric text, BUFR, and GRIB productsx, that we currently produce, and no WMO or AWIPS headers are changing. In the text products, all references to AVN MOS have been changed to GFS MOS, and all references to MRF MOS have been changed to GFSX MOS. For the elements of max/min temperature, spot temperatures, dewpoints, POP, QPF, and probability of thunderstorms, only one set of equations will be used for projections out to 84 hours. As a result, the forecasts for these elements out to 84-h will be identical in the MAV and MEX products. As a result of these changes, the short-range GFS MOS products will most likely be disseminated approximately 5 - 10 minutes later than they are at this time.

Please see Technical Information Notice #03-43 for the official notification.

II. Changes to Stations: Additions, Deletions, Updates

At this time, MDL is making changes to the stations that are available in the GFS MOS products.
145 new sites will be added to the MAV and MEX text messages. A list of these new sites and their associated WMO and AWIPS headers can be found at

4 Sites are being removed from the GFS MOS system (text and BUFR products) due to their closure. The sites are as follows:

Finally, the call letters for 3 sites will be updated in the GFS MOS text and BUFR products. The sites are as follows:

Please see Technical Information Notice #03-44 for the official notificiation, including the WMO headers for the products that will be affected.


III. Addition of Snowfall Amount Guidance

Categorical forecasts of snowfall amount will be available in the short-range GFS MOS text products for 24-h periods ending at approximately 36i and 60 hours after 0000 UTC; 30 and 54 hours after 0600 UTC; 24, 48, and 72 Hours after 1200 UTC; and 42 and 66 hours after 1800 UTC. In the extended-range GFS MOS text products, the categorical forecasts are available for 24-h periods ending at approximately 48, 72, 96, and 120 hoursafter 0000 UTC. Snowfall amount forecasts will be available from September 1st through May 31st. The snowfall amount categories are as follows:
0 = no snow or a trace expected;
1 = > a trace to < 2 inches expected;
2 = 2 to < 4 inches;
4 = 4 to < 6 inches;
6 = 6 to < 8 inches;
8 = 8 inches or more.
Sample messages with snowfall amount for all 4 cycles are available in the Technical Procedures Bulletins for our text products. Please note that at this time, the TPBs have not been updated to reflect the unified MOS system. When the TPB's have been updated, they will be posted on the website

Short-range GFS MOS MAV text products TPBs:

Extended-range GFS MOS MEX text product TPB:


IV. New Equations

At this time, MDL will implement new MOS forecast equations for max/min temperature, spot temperatures and dewpoints, POP/QPF, wind speed and direction, ceiling height and total sky cover, and probability of precipitation characteristics (POPC), in addition to the new snowfall amount equations in section III.


V. Changes to Experimental Ensemble MOS

At this time, we will not be making all the changes necessary to run the Ensemble MOS in the unified GFS paradigm. The Ensemble MOS forecast equations will not be updated on December 16th, instead they will continue to run with the pre-December 16th operational MRF MOS forecast equations. Therefore, the operational extended-range MOS forecasts will be created by using different forecast equations from the 11 ensemble runs. We will not be adding the 145 new sites to the ensemble messages, but we will be removing the 4 sites listed above, as well as PAAK and PAWN, and changing the call letters of the 3 sites. The header line of the ensemble MOS messages will continue to read "MRF MOS GUIDANCE". We will update the ensemble MOS system when time and resources permit.