Impact of Changes to the NCEP Global Forecast System on the Model Output Statistics (MOS) Guidance



On March 6, 2002, NCEP changed the configuration of the Global Forecast System (GFS) to provide four runs of the Global Spectral Model for forecast projections out to 384 hours. Since the changes made on March 6 provide four extended runs of the GFS, NCEP is terminating the MRF, effective April 24, 2002. The impact of these changes on the current suite of AVN and MRF MOS guidance is minimal.

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MDL tested the effects of the GFS resolution change (T254L64 GFS Implementation) on the MOS guidance.


During a 3-month period from December 13, 2001 to March 15, 2002, MDL tested the effects of the GFS resolution change on the MOS guidance by using the output of the parallel 0000 UTC GFS run in the MRF MOS max/min temperature and PoP forecast equations. For max/min temperature, the mean absolute errors (MAE) of the test (or parallel) runs were nearly identical to those of the operational MRF MOS guidance at all projections, although a slight decrease in the MAE of the parallel MRF MOS can be seen in the forecast projections of 96 to 192 hours. For PoP, the Brier scores (or mean sqare errors) of the parallel and operational guidance were also approximately identical; yet a very slight decrease in the Brier score was evident in the test runs for projections of 108 to 144 hours. These minor differences in the operational and parallel MRF MOS guidance packages are not significant. Thus, when the resolution of the GFS is change, the foreast should see little or no difference in the MOS forecast quality.


Verification Results of Resolution Change (T254L64)

 
MDL tested the effects of the GFS change on the MOS guidance.


During a 3-week period in March 2002, MDL tested the effects of the GFS change on the MOS guidance by using the new extended 0000 UTC GFS run initialized at 0245 UTC in the MRF MOS max/min temperature and PoP forecast equations. For max/min temperature, the mean absolute errors (MAE) of the test runs were nearly identical to those of the operational MRF MOS guidance at all projections. For Pop, the Brier scores (or mean square errors) of the parallel and operational guidance were also approximately identical. Minor differences in the operational and parallel MRF MOS guidance packages are not significant. When the MRF is discontinued, MDL will continue to produce extended-range guidance during the 0000 UTC forecast cycle. No changes will occur in the AVN or MRF MOS guidance packages. In the short term, the nomenclature of calling the latter package the "MRF MOS" guidance will be retained.


Verification Results
 




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Last Updated May 9, 2002