Can total lightning data help give warning lead time for non-supercell tornadoes?

Cloud-to-ground lightning has been available for many years and is part of the National Weather Service (NWS) data displayed on AWIPS workstations at the local Weather Forecast Office (WFO). Total lightning refers to the combination of in-cloud lightning and cloud-to-ground lightning, and is a newer data set that until recently was only available in selected areas that had experimental networks or Lightning Mapping Arrays (LMAs). Researchers over the years have tried to relate lightning data to severe weather, including tornadoes, but the relationships have in general been uncertain, in large part to the fact that cloud-to-ground lightning often maximizes in the downdraft phase of a convective storm. What is intriguing about measurements of in-cloud lightning is that it increases in proportion to updraft strength. This connection has prompted much research associating measurements of in-cloud lightning increase (the “lightning jump”) to severe weather, the main hypothesis being that a storm with a rapidly increasing updraft will likely become severe, and indeed studies have shown some significant potential lead time for severe hail producing storms. A potential connection has also been put forth for tornadoes, but here the relationship is not as straightforward, at least for tornadoes associated with supercells, where research through the VORTEX field studies has revealed that tornado production is a complex process. There is a more “simple” type of tornado, however, that occurs during the updraft phase of the convective cell; the non-supercell (or “landspout”) tornado.

Much research, mostly done in the 1980s, established that the non-supercell tornado occurs as an incipient low-level circulation, typically pre-existing along a boundary and often before any storm forms, is stretched in the vertical by the updraft of a cell growing over the low-level circulation. It stands to reason then that observations of the behavior of in-cloud (or total) lightning may be more closely related to non-supercell tornado formation then to more general tornado development, and it is this hypothesis that is examined in this study. Using data from the Colorado LMA and two fortuitously placed non-supercell tornadoes (one near the Cheyenne NWS Doppler radar and the other over the Denver International Airport in close proximity to both the Denver NWS and Denver Terminal Doppler radars) that occurred during the summer of 2013, we will compare the behavior of total lighting in time to the development of the circulations leading up to the tornadoes. Warning lead time for non-supercell tornadoes remains an issue, since the incipient circulation is found at low-levels and can be difficult to detect unless the radar is close to the developing storm. If there is some value to be gained through monitoring total lightning, this could potentially assist the forecaster in issuing a warning for non-supercell tornadoes. These two cases allow for direct comparison of the behavior of the circulation leading up to the tornado, since they were close to the radar, with the tendencies of total lightning, as both cases were within the CO LMA. Total lightning will be available as one of the satellite-derived products in the GOES-R era (the first satellite scheduled for launch in late 2015), so establishing a potential relationship between total lightning and non-supercell tornado development would be of interest to forecasters nationwide.