21st Conf. on Severe Local Storms


A Preliminary Investigation of Supercell Longevity

Matthew J. Bunkers, NOAA/NWSFO, Rapid City, SD; and J. S. Johnson, J. M. Grzywacz, L. J. Czepyha, and B. A. Klimowski

One of the components of the supercell definition includes persistence, namely, that the storm's circulation persists for at least 30-45 minutes. In some cases, a supercell may persist in a quasi-steady manner for several hours, and in extreme cases, the lifetime of a supercell may extend well beyond 4-5 hours. These long-lived supercells can produce significant severe weather along the majority of their paths, and on occasion, they generate a devastating combination of large hail and damaging winds.

Since these long-lived supercells are rare, they present a forecasting challenge. However, a few studies have addressed forecast issues related to supercell longevity. Some of the environmental parameters used to investigate supercell longevity have included storm-relative helicity (SRH), lifted condensation level (LCL) height, midtropospheric dryness, and the synoptic weather regime. No solid relationships have emerged from these studies, which leaves unsolved the problem of why a few supercells persist for many hours.

In the current study, we present findings from a preliminary investigation of supercells that persisted in a quasi-steady manner for greater than four hours. Specific attention is paid to local sounding parameters and the large-scale environment. For comparison purposes, we also examine shorter-lived supercells to determine if the environmental signals are the same or different from their longer-lived counterparts. The main finding of this preliminary work is that the large-scale environment plays a more significant role in determining supercell longevity than what can be inferred from individual soundings.

extended abstract  Extended Abstract (168K)

Session 16, Tornado and Severe Storms Environments
Friday, 16 August 2002, 8:00 AM-9:59 AM

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