Analysis of IC and CG Lightning with Winter Precipitation

In April 2006, Vaisala, Inc., added low frequency (LF) detection capabilities to their National Lightning Detection Network enabling their customers to view not only cloud-to-ground (CG) lightning flashes, but also in-cloud (IC) lightning flashes. The combination of the full suite of CG and IC flash data is used in this case to determine characteristics of lightning flashes in winter precipitation. In particular, we employ flash data from the midwestern winter storm of 01 December 2006. Thundersnow for this event was first observed at 1300 UTC on 29 November 2006 and lasted 48 hrs through 1300 UTC 01 December 2006. In that time frame, 85859 lightning flashes were observed in the United States. Of that total, 8.5%, or 7329, flashes were associated with winter precipitation. Of those lightning flashes, 2974 were detected as IC while 4355 were detected as CG. Further, 3974 of those were detected as negative CG flashes with a mean peak current of -17 kA while 381 flashes observed were positive CG with a mean peak current of 45.7 kA. The range of peak currents extended from -180 kA to +254 kA. although winter precipitation, particularly thundersnow, is thought to be dominated by positive lightning flashes, this analysis indicates otherwise.