21st Conf. on Severe Local Storms


Tornado signatures and precursor activity from 3-D lightning mapping observations

T. Hamlin, New Mexico Institute of Mining and Technology, Socorro, NM; and J. D. Harlin

Observations have been obtained of the total lightning activity in several tornadic storms, first in central Oklahoma during the 1998 MEaPRS project and subsequently in northwestern Kansas and eastern Colorado during STEPS 2000. In each of three or four cases the initial tornado of the storm (or a funnel cloud that did not extend to ground) was accompanied by a distinctive lightning-free region, or lightning `hole', in 3-dimensional observations of the VHF lightning radiation sources. The lightning holes appear to be associated with the strong updraft on the upshear side of the storm, and the tornados occurred on the western edge of the holes. The occurrence of the lightning holes in these and other severe supercell storms was accompanied by upward moving, high-altitude lightning events indicative of strong convective surges in the storm. The F1 tornado on June 29, 2000 of STEPS was preceded by a sequence of three such convective surges at 10 to 15 minute intervals extending up to 15-16 km altitude MSL. Each surge was accompanied by a successively stronger lightning hole, with the third surge initiating the tornado. The observations appear to be characteristic of tornadic storms, or of storms having the potential for becoming tornadic, and could provide an additional means of nowcasting tornado occurrences. Animations of the overall storm activity show the potential utility of lightning mapping observations for monitoring storm severity.

extended abstract  Extended Abstract (592K)

Session 11A, Lightning Studies
Wednesday, 14 August 2002, 4:30 PM-6:00 PM

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