Pre-Convective Environmental Conditions Indicative of Non-Tornadic Severe Thunderstorm Winds over Southeast Florida.

A model was developed which is representative of the synoptic-scale atmospheric conditions present in 1200 GMT upper air data prior to the development of non-tornadic severe thunderstorm winds over Southeast Florida. Scatter plot graphs were utilized to evaluate various stability indices and atmospheric features represented by continuous variables. Storm potential criteria were established using variables which distinguished days with severe thunderstorm wind events from other days. These criteria comprised the development of an initial model based on the analysis of many atmospheric features for the 459 day period of May through September of 1976, 1977, and 1980. All twelve dates selected by the initial model had reports of serve thunderstorm activity, but independent testing using data from May through September of 1978, 1979, and 1981 showed that the model was too restrictive. Less stringent criteria were established and incorporated into a relaxed model. The relaxed model accounted for all dates with a report of non-tornadic severe thunderstorm winds over Southeast Florida when applied to all six thunderstorm seasons 918 days. The pre-convective environment associated with non-tornadic severe thunderstorm winds over Southeast Florida is characterized by instability, little directional wind shear, and northwesterly flow in the mid-troposphere accompanied by potentially cool, dry air. Unfortunately, the unreliable nature of storm reports, and our inability to obtain a more thorough measurement of the atmosphere over the peninsula, make it virtually impossible to construct a perfect model.