Development of a Thunderstorm Algorithm from Very High Resolution AFWA MM5 Data

The HQ Air Force Weather Agency (AFWA) Technology Exploitation Branch (DNXT) has developed a precipitation type product derived from AFWA MM5 data run for various domains at 45km and 15km horizontal resolutions worldwide. The product utilizes algorithms to determine the precipitation type (thunderstorms, severe thunderstorms, rain, freezing rain, sleet, and snow) where the MM5 has output precipitation. For these resolutions of the MM5, “convective precipitation” output from the Grell convective parameterization scheme (CPS) is used.

For MM5 theaters run at higher resolution, convection is explicitly resolved and a CPS is not required. As a result, the precipitation type product displays rain, freezing rain, sleet, and snow only. DoD users worldwide desired to see thunderstorms added onto the high resolution precipitation type products, and scientists from the AFWA/DNXT and Army Research Laboratory embarked on a project to create a thunderstorm potential algorithm for use in higher resolution domains. Multivariate regression analysis techniques were used on model data collected during Spring 2003 over Southwest Asia. Results provided good candidate algorithms that were in-turn applied to data collected during Spring 2004 for verification. These results will be presented to show algorithm development and verification efforts to include the threshold values best indicative of forecast thunderstorm conditions. Subsequently, a suitable replacement algorithm can compensate for the lack of CPS output of convective precipitation, allowing the display of forecast thunderstorm areas on AFWA’s high-resolution precipitation type product