Evaluation of WRF forecasts of tornadic and nontornadic outbreaks when initialized with synoptic-scale input: The utility of “base-state” parameters

Forecasters frequently analyze predicted and observed severe weather parameters to assess severe weather environments and to determine the types of severe weather that will occur in specific regions. However, numerous studies have suggested that certain synoptic and subsynoptic environments may favor particular convective modes, which often have profound impacts on the types of severe weather subsequently observed. This makes the analysis of “base-state” parameters, such as geopotential height, wind speed and direction, dew point temperature (or relative humidity), etc., at various levels of the atmosphere, potentially very useful in the prediction of severe weather.

An analysis of base-state parameters, both subjective and objective, using simulations of 50 tornado outbreaks and 50 primarily nontornadic outbreaks from the Weather Research and Forecasting mesoscale model (WRF), initialized with synoptic-scale data, will be presented. Results indicate that geopotential heights and wind speeds/directions, at various levels in the atmosphere, can be used to distinguish outbreaks consistently. Comparisons with the analyses of severe weather parameters suggest that the use of some base-state parameters may be as beneficial in the accurate diagnosis of outbreak type. The implications of this study, particularly on the importance of synoptic- and subsynoptic-scale patterns in the determination of outbreak types, will be discussed.