Low Topped Convection and Total Lightning Observations from North Alabama

Total lightning observations from the North Alabama Lightning Mapping Array (NALMA) have been used in operations with the Huntsville National Weather Service office since 2003. In a partnership with NASA's Short-term Prediction Research and Transition (SPoRT) Center, observations from this very high frequency (VHF) detection network are used for several activities. Predominantly, the NALMA data are used to enhance the situational awareness of forecasters which in turn leads to a better analysis of storm intensification and improved severe thunderstorm and tornado warnings. Total lightning observations also are used in lightning safety situations aiding with airport weather warnings alerting to the threat of imminent lightning activity.

The training that SPoRT provides on the use of NALMA data, as well as data available from other networks, emphasizes lightning jumps as precursors to severe weather. Specifically, a lightning jump is a rapid increase in total lightning activity, which is strongly related to the updraft strength of the thunderstorm. This is used to great effect in numerous severe weather warning events. However, lightning jumps do not always precede severe weather manifestation, and there are several notable cases where this has not occurred. In particular are events from 6 May 2009 and 21 January 2010. In each case a thunderstorm produced an EF-2 rated tornado with very little total lightning observed. Both cases occurred just outside (6 May) or in (21 January) Huntsville, which is in the heart of the NALMA network and therefore has no detection efficiency issues. Analysis of these two events demonstrates that these were low-topped thunderstorms. Here the lightning production was limited as the updraft did not extend into the mixed phased region where charging primarily occurs. This presentation will take a preliminary look at the two low-topped convection events just mentioned, along with several other cases that serve as a “null” set of data for using total lightning as a precursor to severe weather. Future research will investigate whether limited lightning production is commonly observed with low-topped convection, or if these are special cases.