Interrelationships among Wind Direction, Atmospheric Moisture Content and Stability with the Spatial Distribution of Rainfall and the Occurrence of Severe Weather in Pinellas County, FL

Abstract

To improve the operational prediction of local mesoscale phenomena the interrelationships among wind direction, atmospheric moisture content and stability with the spatial distribution of rainfall and the occurrence of severe weather in Pinellas County in west central Florida was examined. This peninsular county has some unique topographic features and sea breeze patterns that cause forecast challenges. The 1200 UTC soundings taken at Ruskin, Florida during June-August, 1995-2009 we used to first identify the predominate wind directions over the county. The sounding data were then used to further classify days by moisture content (i.e., total precipitable water) and thermodynamic stability (i.e., Convective Available Potential Energy). Composite precipitation maps were then produced. The primary influence of rainfall distribution was wind direction, with less rain falling over the peninsula on days with westerly flow than those with easterly flow. Moisture and stability had secondary effects on the location and amount of precipitation in the county. An operational guide was developed to help forecasters develop more accurate quantitative precipitation forecasts. The likelihood of severe weather was also related to wind direction, with more events occurring during easterly flow than westerly. The most significant severe weather cases were examined to determine the influence of sea breeze and outflow boundary interactions, and also the development and vertical extent of the convection, leading to rainfall and severe weather over the county. The identification of such high impact events (tornadoes, downbursts, hail, and waterspouts) are of particular interest and an operational guide and Graphical Forecast Editor Smart Tool were developed to provide information to forecasters of the possibility of severe weather