Monday, 3 August 2015
Back Bay Ballroom (Sheraton Boston )
Just after sunset on 5 October 2014, convection initiated over parts of northern Oklahoma and northwestern Arkansas along a stalled front that was reinforced by a cold pool from earlier daytime convection in Kansas. The cells developed into a long-tracked mesoscale convective system (MCS) that propagated southward and eventually reached the Gulf of Mexico the following afternoon. The MCS produced one tornado and several severe wind and hail reports throughout its lifecycle. The WRF-ARW model, surface observations, and radar data are utilized to examine how the system evolved from surface-based to elevated owing to nocturnal cooling, and the subsequent evolution of the system back to surface-based as diurnal heating resumed the following day.
Previous studies have examined how dynamical lifting along gust fronts and the upward-directed perturbation pressure gradient force owing to embedded circulations can result in at least partially surface-based storms even in the presence of a surface-based stable layer. These mechanisms can result in an environment conducive to nocturnal tornadogenesis assuming surface-based convective available potential energy (CAPE) exists and the near-surface air can be lifted to its level of free convection (LFC). These conditions are evaluated to determine the significance of near-surface lifting throughout the duration of the convection, especially in the vicinity of the tornado, and into the daytime hours. System maintenance via lifting of layers to their LFCs by bores is also investigated, especially when lifting by a surface cold pool is no longer important.
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