Wednesday, 29 October 2008
Madison Ballroom (Hilton DeSoto)
The outbreak of 12 March 2006 featured several long-lived supercells that produced a disproportionate amount of the severe weather during the event. The longest-lived supercell formed in northeast Oklahoma, and thirteen hours later merged with a developing quasi-linear convective system in north central Illinois. It produced tornadoes throughout Missouri and Illinois, the strongest of which was an F2 near Springfield, Illinois. This supercell was also a prolific large hail producer throughout its life cycle. The mesoscale conditions that supported this unique evolution, including the extreme longevity of the supercell, were examined using real-data simulations with the Weather Research and Forecasting (WRF) model.
The WRF simulation successfully replicated convective initiation, convective mode, and the existence of a long-lived supercell. We found that the movement of the extratropical cyclone aided in sustaining mesoscale conditions favorable for supercell organization. In particular, the warm front was associated with an extensive corridor of CAPE and shear within which the long-lived supercell tracked. This simulation also provided an opportunity to use model output to quantitatively evaluate the presence of supercells. We found that a normalized product of vertical vorticity and vertical velocity correlated well in location with mesocyclones identified by Doppler radar and also with tornado reports.
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