18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Wednesday, 1 August 2001
The behavior of low-level vorticity and circulation surges of a modeled supercell
Brian J. Gaudet, Colorado State University, Fort Collins, CO; and W. R. Cotton
Poster PDF (91.0 kB)
On 8 Jun 1995, a series of supercells produced severe weather in the Texas and Oklahoma Panhandles. The synoptic weather features of the day included a surface front extending to the southwest across central Kansas towards the extreme western Oklahoma Panhandle, and a dryline extending to the south from the front within the Texas Panhandle. A number of the supercell storms were well studied by the Verification of the Origins of Rotation in Tornadoes EXperiment (VORTEX), including tornadic storms near Kellerville and Allison. The first major storm of the day developed near Elmwood, Oklahoma, near the intersection of the surface front and the dryline. This particular storm produced large hail, but failed to produce any significant tornado despite evidence of significant mesocyclonic circulation aloft.

The Regional Atmospheric Modeling System (RAMS) was used to simulate the synoptic weather conditions of the Elmwood storm. The simulation was initialized and nudged using the Rapid Update Cycle (RUC) product of the Mesoscale Analysis and Prediction System (MAPS). Surface station reports were also incorporated into the initialization. The model uses mixed-phase bulk microphysics and represents surface exchange processes using the Land Ecosystem Atmosphere Feedback model, version 2 (LEAF-2). Longwave and shortwave radiative transfer incorporates the effects of water condensate and exchanges between vegetation and canopy air. Further simulations are performed with nested grids introduced into the synoptic-scale grid to capture the evolution of individual supercells. These are compared to simulations performed in horizontal-homogeneous environments, based on both model and VORTEX-derived soundings in the vicinity of the Elmwood storm. The influence of environmental heterogeneity on the evolution of the storms is examined.

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