1.4 Convection Initiation along the Outflow Boundary of the 15 July 2015 Nocturnal MCS in Western Kansas

Tuesday, 9 January 2018: 9:15 AM
Room 6A (ACC) (Austin, Texas)
Coltin D. Grasmick, Univ. of Wyoming, Laramie, WY; and B. Geerts

A wide, moderately intense MCS that formed over eastern Colorado and moved into western Kansas during the night of 15 July 2015 produced a persistent, well-defined outflow boundary on its eastern edge. This boundary often peeled away far enough from the MCS echoes that it could be studied with profiling lidars aboard the University of Wyoming King Air (UWKA). New convective cells repeatedly formed east (upshear) of the boundary and then merged with the MCS precipitation. Thus this convection initiation (CI) was instrumental in MCS propagation and maintenance.
The question addressed in this presentation is how upstream low-level air parcels were sufficiently displaced vertically to trigger new convective cells. The water vapor and aerosol backscatter information from the UWKA Compact Raman Lidar (looking down) and the Wyoming Cloud Lidar (looking up) allow determination of the vertical displacement of the most-unstable air parcels, and characterization of the vertical structure of the stable boundary layer and the outflow boundary in transects across this boundary. We find that in some locations, the outflow boundary has characteristics of a density current, while elsewhere it shows signs of an undular bore and even a solitary wave structure. Any of these dynamical structures allow CI in this case.
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