This talk will report on the preliminary results of a comprehensive study of cool season tornadoes in the southeast United States. Previous research has shown that there is a relatively high frequency of tornadoes in the overnight to early-morning hours during the cool season in the Southeast, particularly in areas close to the Gulf of Mexico. In fact, most strong and violent tornadoes (F2 or greater) in Florida occur during the cool season, associated with extratropical cyclones. The cause of this nighttime maximum during the winter months is not well understood, and one focus of this research will be on gaining a better understanding of the causes of this phenomenon.

Previous research has also documented the importance of return flow of warm, moist tropical air across the Gulf region after the passage of cold fronts through the Gulf in the development of potential severe weather scenarios along the Gulf coast. The warm Loop Current in the Gulf also can increase fluxes of heat and moisture into this return flow air, which can lead to rapid air mass destabilization. It has also been shown, however, that forecasting the trajectories of return flow air is difficult, and that operational numerical prediction models are not able to accurately forecast the modification of the boundary layer (partially due to lack of data over the Gulf), which can be important in determining the severe weather potential over the Southeast.

The focus of this talk will be on the importance of mesoscale processes in the evolution of the tornadic central Florida squall line of 22-23 February 1998. Preliminary results suggest that differential diabatic heating contributed to frontogenesis and ascent in the vicinity of a strong low-level baroclinic zone located over the northern Florida peninsula. The baroclinic zone was reinforced on its poleward side by both rain-cooled air and a northeasterly fetch of air that passed over anomalously cool sea surface temperatures east of Georgia and northern Florida, and reinforced on its equatorward side by a surge of warm, moist air flowing up the Florida peninsula. The resulting strong baroclinic zone may have played a significant role the rapid squall line intensification as it made landfall on the Florida peninsula.

Additionally, the role of the sea surface temperature anomalies in and around the Loop Current appear to have modified the low-level heat and moisture fluxes into the storm system as it crossed the eastern Gulf, and thus directly impacted the intensity of the convection, causing it to strengthen (weaken) over the warm loop current (in the cool waters off the west coast of Florida). The case study will be used to illustrate key issues being addressed by this research, especially focusing on the evolution of the dynamics and thermodynamics in the boundary layer in the vicinity of the tornado event.