Defining Predictors for the Timing of Mesoscale Thunderstorms During Florida’s Convective Season
Urleen Jones
Michael R. Witiw
Florida Institute of Technology
Tony Cristaldi
Dave Sharp
National Weather Service Forecast Office
Melbourne, Florida
During the warm season in Central Florida, convection is enhanced by convergence of the East Coast Sea Breeze (ECSB) and the West Coast Sea Breeze (WCSB). Several studies have shown that the Florida sea breeze front supports a narrow band of convergence and upward motion of the local air mass. However, the presence of the sea breeze on any given day does not necessarily entail that thunderstorms will occur.
Due to day to day variations in thermodynamic properties, the meteorologist must rely on unconventional data for forecast guidance (Chelius & Frentz, 1992). This unconventional data includes assessment of sea breeze interaction with the synoptic scale flow, as well as the influence of surface properties on its development. The forecaster then makes a qualitative assessment of unconventional data based upon experience.
Airmass, or mesoscale thunderstorms are a common occurrence at Orlando International Airport (MCO) during the summer season. These phenomena present a flight safety hazard to both commercial and general aviation. Furthermore, delays due to this convective activity, can result in increased airport congestion on thunderstorm days.
For these reasons, it is essential that Terminal Area Forecasts (TAF) are timely and accurate as possible. In seeking a quantitative basis for inclusion of the effects of the sea breeze on thunderstorm activity, input parameters must be readily available to the meteorologist at the time of the forecast. This study uses a conventional statistical approach in determining appropriate input parameters to aid in forecast of onset time and duration of thunderstorm activity. Historical rawindsonde data used in this study were from Ruskin (TBW) and Cape Canaveral (XMR) for the years 1994 through 1997. Only mesoscale convective events were analyzed. Thunderstorm data were filtered to exclude storms induced by synoptic scale fronts or tropical disturbances. Multiple regression techniques were used and several variables were tested including 1000 meter winds, precipitable water, convective available potential energy (CAPE) unmodified, a CAPE modified to eliminate normal 1200Z temperature inversions, and various measures of instability. A step wise regression was used entering the most highly correlated variable first. Early results show the unmodified CAPE and the 1000 meter east wind component to be significant as predictors for thunderstorm onset time.
The 8th Conference on Aviation, Range, and Aerospace Meteorology