Verification Results from the Northeast Probabilistic Storm Total Snowfall Forecast Experiment During Winter of 2014-2015

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. Approximately 30 forecast points were selected for verification over all four WFO county warning areas for numerous events, including the 26-27 January 2015 blizzard, the early February 2015 Boston blizzard, and several other events. The probabilistic forecasts were verified against storm total snowfall reports from WFO Public Information Statements and/or computed from CF6 reports. 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.