Evaluation of ensemble icing probability forecasts in the NCEP SREF and VSREF systems

Ensemble icing product in both Short Range and Very Short Range Ensemble Forecst Systems (SREF and VSREF) at NCEP has long been generated but not been verified or evaluated with truth yet due to a lack of appropriate observational icing data. Recently, gridded format icing data from AWC's Aviation Digital Data Services (ADDS) have been available to NCEP. The ADDS gridded data include analytical current icing potential (CIP) and forecast icing potential (FIP) at various flight levels with different products including total icing probability, SLD, and icing severity. In this study, the CIP severity (seen as a truth event) data are used for the icing ensemble probability verification based on so called "Event-Probability", or "E-P", verification capability built in NCEP's grid-to-grid verification system. The resolution of CIP is 20 km, which is different from the resolutions of both VSREF (13 km) and SREF(32 km). To do the grid to grid verification, both VSREF and SREF's icing probability forecasts are first interpolated down to the 20km ADDS grid, then do the E-P grid-to-grid verification in both deterministic and probabilistic aspects. This paper gives a brief summary of how this work was done over CONUS with nearly one month data and the verification results.