Wednesday, 13 January 2016
During the winter months of 2014-2015, four WFOs in the Eastern Region of the NWS conducted an experiment in producing probabilistic storm total snowfall information as a means to communicate uncertainty in the forecast. The forecast technique, developed at WFO Sterling, utilizes NOAA/NWS WPC's probabilistic snowfall range as a first guess and produces a probability distribution function centered about the official WFO storm total snowfall forecast. Tenth, 50th and 90th percentile values, exceedance probabilities, and categorical range probabilities for a variety of thresholds are output as a result with each forecast update, and made available to end users for use in decision making. The probabilistic forecasts were verified against storm total snowfall reports from WFO Public Information Statements and/or computed from CF6 reports for numerous events, including the 26-27 January 2015 blizzard, the early February 2015 Boston blizzard. Several statistical metrics including percentile bias, percent correct within the 10th-90th range, and ranked probability scores were computed and analyzed to assess overall accuracy and forecast trends through the experiment period. Early results indicate that the technique demonstrates statistical reliability. Feedback from emergency managers as well as the general public indicates that the probabilistic snowfall information was well received and appeared to be understood.
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