David Harrison- March 15

Utilizing the High-Resolution Ensemble Forecast (HREF) to Produce Calibrated Probabilistic Thunderstorm Guidance at the Storm Prediction Center

David Harrison

Friday, March 15^th

3:30pm/NWC 5600

In 2003, the Storm Prediction Center (SPC) began post-processing the National Centers for Environmental Prediction (NCEP) Short-Range Ensemble Forecast (SREF) system to provide operational guidance on the prediction of lightning hazards across the contiguous United States.  This guidance relies on physically-based parameters to produce probabilistic forecasts of thunderstorms, which are then calibrated using data from the National Lightning Data Network (NLDN) such that the predicted probabilities from an independent sample are statistically reliable against the verifying NLDN data.  Although this method has generally shown both skill and reliability at predicting the occurrence of lightning, the temporal and spatial accuracy of the predictions is limited in part by the inability of the SREF to explicitly resolve convection.  This study serves as a preliminary investigation into the use of the operational CAM ensemble at NCEP, the High-Resolution Ensemble Forecast (HREF), for potentially improving probabilistic lightning prediction via the inclusion of simulated radar reflectivity and other storm-attribute fields.  Each HREF-member field was compared to the NLDN cloud-to-ground (CG) lightning dataset between 1 July 2017 and 1 July 2018 to identify which fields most closely correlated with the occurrence of one or more CG lightning flashes.  A statistical model was then derived from the most correlated fields and optimized using a grid-search technique.  Finally, probabilistic thunderstorm forecasts were computed from the HREF using the optimized model and calibrated to be statistically reliable.  This probabilistic guidance has been made available to SPC forecasters via a web-based interface, and is now being experimentally used in forecast operations.