Global thunderstorm guidance forecasts from the AVN Model from the VVSTORM Algorithm

GLOBAL THUNDERSTORM GUIDANCE FORECASTS FROM THE AVN MODEL FROM THE VVSTORM ALGORITHM

A large organization of professionals helps domestic aviation operations in the United States avoid hazardous weather. As international operations have expanded, so has increased the need for similar support for global hazardous weather avoidance. Two factors complicate international aviation weather forecasting. First, many flights are over data sparse oceans, so there is less knowledge of the state of the atmospheric conditions that cause hazardous aviation weather. Second, international flights are typically much longer than domestic flights which increases the necessary forecast lead time of hazardous weather areas for effective flight planning.

Thunderstorms are the primary hazard at international flight altitudes. Forecasting thunderstorms in general is rather simple conceptually; find the areas in which potentially unstable air parcels can be lifted to their Level of Free Convection. Developed for domestic thunderstorm forecasting guidance, the experimental VVSTORM algorithm examines numerical model output for favorable conditions for thunderstorms using this simple recipe. Since VVSTORM was designed to run on any numerical model resolution through its parameterization of parcel lifting, the Aviation Weather Center began experimenting with VVSTORM on the global AVN numerical model.

This paper will show comparisons of AVN-VVSTORM output with 1) VVSTORM output from the RUC2 and ETA models for mid-latitude convection over the United States, and 2) satellite imagery for six-hour AVN forecasts over tropical oceans. Subjective experience with AVN-VVSTORM has been very good in the mid-latitudes and good in the tropics. The only apparent problem area is along the equator where the parameterized parcel lifting appears not to force enough convection.