FORECAST PERFORMANCE OF AN OPERATIONAL MESO-GAMMA-SCALE MODELLING SYSTEM FOR EXTRATROPICAL SYSTEMS

In our continuing work on the implementation and applications of an operational mesoscale modelling system dubbed "Deep Thunder", we examine its forecast performance for several events of tropical origin over the Mid-Atlantic and Northeast United States. Initially, this prototype provided nested 24-hour forecasts, which are typically updated twice daily, for the New York City metropolitan area to 1 km resolution. It has been recently extended to also provide forecasts for the Baltimore-Washington D.C. metropolitan area at 2 km resolution. Explicit, bulk cloud microphysics are included in the model predictions for both geographies. All of the processing, modelling and visualization are completed in one to two hours on relatively modest hardware to enable sufficiently timely dissemination of forecast products for potential weather-sensitive applications.

In order to evaluate the quality of the forecasts produced by Deep Thunder at a storm-scale and its potential skill, we have identified a number of interesting cases in which systems of tropical origin impacted regions for which operational model forecasts are performed. While the systems had become extratropical before reaching regions studied, they did retain some of the structure and dynamics of their tropical genesis. We compare the model results with observational data and other available forecasts as well as the operational availability of specific forecast products. Such performance is examined by considering forecast timing, locality, intensity and structure of stratiform and convective rainfall events.