Wednesday, 23 January 2008: 4:30 PM
Severe Weather Precursors in the Lightning Activity of Tennessee Valley Thunderstorms
222 (Ernest N. Morial Convention Center)
Rapid increases in the total lightning activity prior to the onset of severe weather have been observed with both ground-based and satellite lightning detection systems. However, the connection between this pronounced total lightning trend, storm kinematics and severe weather is not well understood. To further understand this connection, the total lightning activity of twenty tornadic and non-tornadic thunderstorms that occurred across southern Tennessee and northern Alabama was compared with radar reflectivity and Doppler-derived velocity, shear, and momentum. Also, an algorithm was developed to detect the rapid increases in the lightning activity and quantify their utility in severe weather identification. Nearly all severe storms studied produced total flash rates in excess of 60 flashes min-1 and lightning jumps, characterized by rapid increases in total flash rate. In the tornadic thunderstorms, the lightning jump is the dominant electrical response during tornadogenesis. Lightning jumps used alone as a severe weather predictor resulted in a probability of detection of 0.985, a false alarm rate of 0.446, and critical success index of 0.549. Furthermore, these lightning jumps were found to precede descending and non-descending tornadoes by 18 to 28 min.