Recent studies have suggested that Weather Research and Forecasting mesoscale model (WRF) forecasts are capable of discriminating tornado outbreaks from primarily nontornadic outbreaks consistently at least 72 hours in advance of their occurrence and when initialized with coarse, synoptic-scale data. However, many primarily nontornadic outbreaks occur during the summer months, when tornado outbreaks rarely are observed. It is reasonable to hypothesize that the WRF may not be able to distinguish the outbreak types if the cases are limited to those occurring in the spring and fall seasons, when both types of outbreaks are common.

In this study, WRF simulations of 50 tornado outbreaks and 50 primarily nontornadic outbreaks are conducted, using the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis datasets. Analyses of the 24-hour forecasts, in comparison to previous research in which the primarily nontornadic outbreaks were not limited to the spring and fall seasons, indicate that there is only limited degradation in the model's ability to discriminate outbreak types when limiting the cases to those occurring in the spring and fall. These results suggest that synoptic-scale processes play a substantial role in the occurrence or absence of tornado outbreaks. The analysis of these cases also indicates that the outbreak types frequently consisted of noticeably different synoptic and subsynoptic environments. The utility of various severe weather parameters and the seasonal dependence of several of these variables will be discussed.