Total lightning is often useful for situational awareness heading into the heart of the Southeast convective season. Typically, by late May, nearly all echoes on radar are producing lightning, and data from the North Alabama Lightning Mapping Array (NALMA) help to assess which of the cells require further attention.
This year was a little different.
On several days during the last week of May, a subtle warm layer and large dry layer aloft helped to cap the atmosphere, or at least limit vertical growth, across northern Alabama and southern middle Tennessee. We observed scattered “thunderstorm” development with 50 dBZ echoes at 0.5 degree elevation–but higher radar tilts yielded very limited vertical structure with these cells (very low reflectivity beyond about 2.4 degrees). While reviewing data from the NALMA, we realized that total lightning was giving us a clue–few, if any of these cells had any total lightning at all, as you’d expect with such shallow convection. The stronger cells with greater vertical depth (warranting further interrogation) were the only ones producing any total lightning whatsoever.
So, in this situation, total lightning data still provided situational awareness–but in a slightly different way. Instead of looking for the storms with the greatest flash rates or source densities (or changes thereof), we were looking for storms with ANY flashes or sources. However, since then, we’ve been aboard the Mesoscale Convective System train, and we’ve returned to our traditional uses of NALMA data.)