Visualization and Quantitative Assessment to Verify Precipitation Forecasts Associated with Mid-Latitude Cyclones across the Eastern United States

Abstract

Analysis was conducted to verify forecast against observation precipitation associated with mid-latitude cyclones over the Eastern US in winter and spring 2013 using Geographic Information Systems (GIS). The forecast data are day two 24-hour Quantitative Precipitation Forecasts (QPF) produced by the Global Forecast System (GFS) model. The analysis methods produced categorical geographic error maps of hits, misses and false alarms in spatial relation to the mid-latitude cyclones and traditional verification scores for each day. A hypothesis test was also performed to determine if the GFS mean forecast precipitation over the study area is significantly different from the mean observed precipitation during mid-latitude cyclones. The spatial verification maps, as an analytical and visualization tool, provided evidences on geographical relationship between correct predictions (hits and correct negatives) and incorrect predictions (misses and false alarms).  Working together with quantitative scores and hypothesis test, spatial verification maps reveal that the GFS model has a tendency to over forecast precipitation coverage associated with mid-latitude cyclones over the Eastern US and often moves the mid-latitude cyclones too fast.