Forecasting sea breeze enhanced thunderstorms at Eglin Air Force Base: A comparison between empirical methods and the high resolution rapid refresh model

Summer thunderstorms pose the greatest forecast challenge for the United States Air Force's 96th Weather Flight (96 WF) which provides weather support for the Department of Defense's largest Air Force installation, Eglin Air Force Base. Located on Florida's panhandle, Eglin Air Force Base encompasses 834 thousand square miles of land and water ranges. Due to the base's coastal location with unique coastline geometry, sea breeze is a dominant forecast consideration for summer thunderstorm initiation. The 96 WF currently utilizes an empirical thunderstorm forecast method developed by former staff meteorologist Mr. Roger Winn during the summer of 1986. WINNDEX combines the use of 12 UTC model soundings and nomograms to provide a rain shower or thunderstorm forecast for Eglin's main base or its 724 square mile land range. In a March 1993 Air Force study verifying WINNDEX accuracy, convective rain showers or thunderstorms, were correctly predicted 69% of the time on the Eglin range and 64% of the time on Eglin's main base location based on activity occurring at some point during the day. This included a false alarm rate of 21% for the Eglin range and 26% for Eglin's main base. This current study seeks to compare the National Center of Environmental Prediction's (NCEP) High Resolution Rapid Refresh (HRRR) model, to the skill of the empirically developed WINNDEX over the summer season of 2015 from May through September. Preliminary results indicate the HRRR's lightning threat product to have potentially improved skill over WINNDEX with 76.8% and 76.0% correct forecasts for lightning occurrence for the Eglin range and Eglin's main base respectively. Additionally, early results of the HRRR's composite reflectivity output indicates good skill for the Eglin range with 82.3% correct for convective activity, but a lower skill for Eglin main with only 53.2% correct forecasts. These preliminary results indicate that high resolution modeling may improve forecast skill over empirical methods at Eglin where complex coastal geometry and resulting sea breeze circulation dominate local flow. Further research will examine initial rain shower and thunderstorm onset timing error comparing the HRRR model and WINNDEX methods.