March 4, 2008

New MOS forecast equations based on output from NCEP’s North American Mesoscale Model (NAM) have been developed for selected weather elements. Thus far, the new guidance is available for maximum, minimum, and 2-m temperature, dew point, probability of precipitation (POP), and wind speed and direction. We have used 2-season dependent data samples for these new NAM MOS elements. However, since the NAM had been running in the current WRF-NMM configuration for only a few months prior to system development, both the warm- and cool-season dependent samples for the NAM MOS contain a mixture of data from the older, eta-coordinate model and the WRF-NMM in its latest two operational configurations. Despite this, the new NAM MOS system performs favorably when compared to both the original eta MOS system (applied to eta-model output) and a “hybrid” system whereby the older, eta MOS equations were applied to output from the current configuration of the NMM.

The tables below give the results of cool- and warm-season comparative verifications performed for the above three systems. Verification scores are presented at our standard set of 335 verification sites for the weather elements listed. However, because of the scarcity of available developmental data, these withheld-data tests generally were limited to a period of 30-35 days for each season. Verification results on more extensive samples of independent data will be available as we progress through the spring and summer months of 2008.

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