Making Sense of Snowfall Accumulations in NCEP Models (322)

Geoffrey Manikin, NASA SPoRT / University of Alabama in Huntsville, College Park, MD

Logan Dawson, NOAA/NWS/NCEP/EMC and I.M. Systems Group

Tracey Dorian, NOAA/NCEP/NWS/EMC and I.M. Systems Group



Converting model QPF to actual forecasts of amounts of snow remains a major challenge for forecasters. Attempts have been made to apply snow-to-liquid ratios (SLRs) that are more reasonable and representative than the standard 10:1, but simply determining what amount of model QPF is snow is extremely difficult right at the start. This presentation attempts to help understand how model snow water equivalent is derived and help forecasters understand major discrepancies that often exist between model &ldquosnow accumulations&rdquo and precipitation type. A quick overview of precipitation type computations in the NCEP models will be given. Alternatives to examining snow accumulation maps will also be discussed, including using changes in accumulated snow depth, explicit parameters from sophisticated model microphysics, and alternate SLRs. Applications of these snow accumulation and precipitation type tools to winter storm cases highlighted by EMC's Model Evaluation Group (MEG) will be featured.

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