Generating Probabilistic Severe Timing Information from SPC Outlooks Using the HREF

Storm Prediction Center (SPC) forecasters have demonstrated skill over the past decade in generating probabilistic Convective Outlooks for the entire convective day (i.e., 12-12 UTC). Although adding timing information on the expected severe weather threat to the SPC Outlooks would be a desirable feature, generating this information is challenging without increasing the forecast staff or requiring a significant increase in workload for the forecaster. The recent operational implementation of a convection-allowing model (CAM) ensemble in the NWS, the High-Resolution Ensemble Forecast (HREF) system, has enabled the development of a prototype system at SPC that uses explicit convective timing and evolution details from the HREF in conjunction with SPC Convective Outlooks to generate probabilistic severe timing information. The advantage of this type of system is that it combines the strengths of the human forecast (i.e., location and magnitude of the daily severe weather threat) with the strengths of a CAM ensemble (i.e., explicit hourly probabilistic information on the convective evolution) while maintaining overall consistency with the operational SPC Convective Outlooks. The inputs and algorithm used to generate this probabilistic severe timing information will be discussed along with examples of the output and performance of this real-time prototype system.