Joint Poster Session JP3.10 Winter Weather Guidance from Regional Historical Analogs

Wednesday, 3 June 2009
Grand Ballroom Center (DoubleTree Hotel & EMC - Downtown, Omaha)
Chad M. Gravelle, CIMSS - Univ. of Wisconsin / NWS Operations Proving Ground, Kansas City, MO; and C. E. Graves, J. P. Gagan, F. H. Glass, and M. S. Evans

Handout (3.0 MB)

Effective interpretation of model output requires both knowledge and experience. However, even experienced forecasters can misinterpret model output due to an overreliance on the values and placement of model Quantitative Precipitation Forecasts (QPF) when more attention should be focused on synoptic and mesoscale forcing mechanisms. Conceptual models, composite analyses, and forecast analogs can assist in the identification and analysis of high-impact weather events because atmospheric fields and outcomes are quasi-repeatable. In particular, the knowledge of past events that exhibit similar characteristics to the current forecast can assist forecasters with a range of potential scales and intensities of an upcoming high-impact winter weather event.

Short-term (F036-F072) guidance has been developed that extracts similar past cases to the current Global Forecast System (GFS) output. The analog guidance is produced twice a day (1200 UTC and 0000 UTC) on regional domains in the Midwest and East Coast. These analogs utilize the “perfect prog” approach where the forecast fields are used to search the 28-yr North American Regional Reanalysis (NARR) dataset for potential analogs. Analogs are chosen statistically using spatial correlations and mean absolute errors from twelve atmospheric fields. These fields were chosen based on conceptual models of heavy snow events in the Mid-Mississippi Valley. After the analogs are statistically ranked, probabilistic guidance is created from the top fifteen analogs. The resultant output can assist forecasters in quickly determining both the scale and intensity of similar events, and the range of possible solutions based on these historical events. In addition, experience of past events can be gained by viewing the atmospheric fields and outcomes of the individual analogs. Examples of analog performance and forecaster utility will be shown for both domains (Midwest and East Coast) from the winter of 2008 - 2009.

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