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

The High-Resolution Ensemble Forecast (HREF) calibrated thunder guidance is a suite of probabilistic forecast products designed to predict the likelihood of at least one cloud-to-ground (CG) lightning strike within 20 km (12 miles) of a point during a given 1-hour, 4-hour, or 24-hour time interval. This guidance takes advantage of a combination of storm-attribute and environmental fields produced by the convection-allowing HREF to objectively improve upon lightning forecasts generated by the non-convection-allowing Short-Range Ensemble Forecast system (SREF). Additional products, such as localized point forecasts, can then be derived from the probabilistic guidance. This study will provide an overview of how the HREF Calibrated Thunder guidance was developed and calibrated to be statistically reliable against observed CG lightning strikes recorded by the National Lightning Data Network (NLDN). Performance metrics for the 1-hour, 4-hour, and 24-hour guidance will be provided and compared to the respective SREF lightning forecasts. Finally, several case studies will be reviewed to demonstrate some of the strengths and weaknesses of the new calibrated thunder guidance. The HREF Calibrated Thunder guidance has been implemented operationally at the SPC, and 4-hour probabilistic lightning forecasts are now available to the public on the SPC’s website at https://www.spc.noaa.gov/exper/href/?model=href&product=guidance_thunder_hrefct_004h.