Signatures in Lightning Activity during Tennessee Valley Severe Storms of 5-6 May 2003

This study focuses on the 5-6 May 2003 tornadoes that occurred across the Tennessee Valley. Two storms trekked across southern Tennessee and northern Alabama producing several tornadoes along their path. Data obtained with the North Alabama Lightning Mapping Array (LMA) and National Weather Service Doppler radar was used to analyze the electrical, microphysical, and kinematic evolution of the two storms. The Tennessee storm was a classic supercell that produced a short-lived F3, which exhibited a radar “hook” echo several minutes prior to touchdown. Furthermore, a rapid increase in total lightning activity (or lightning “jump”) occurred prior to the appearance of a large increase in mesocyclone rotation. The second tornadic storm was a high precipitation supercell that evolved into a quasi-linear squall line. It produced several weak tornadoes during its lifetime and exhibited one large lightning jump before developing into a squall line.

Interestingly, a relative maximum in the total lightning activity preceded the occurrence of each tornado, many by 15-20 min. Some of these maxima correspond to increases in reflectivity echoes aloft, supporting previous studies which found a relationship between updraft strength and lightning activity. Also, in the minutes prior to the 5 May 2003 tornadoes, increases in the total flash rate were concurrent with increases of shear at low levels within the storm. Findings suggest a possible correlation between the lightning jump and tornadogenesis.