17.7
Differences in evolution of multiple storms in 8 June 1995 simulation
Brian J. Gaudet, Colorado State Univ., Fort Collins, CO; and W. R. Cotton
On 8 June 1995 a number of severe thunderstorms formed in Texas and Oklahoma on a day characterized by an unusually intense cold front and a dryline in the central Texas Panhandle. The VORTEX-95 (Verification of the Origins of Rotation in Tornadoes EXperiment) field project was present to gather observations on the evolution of a family of tornadoes in the eastern Texas Panhandle, as well as a supercell 'null case' in the Oklahoma Panhandle that produced softball-sized hail but no visible tornadoes.
In this study the Regional Atmospheric Modeling System (RAMS) is used to investigate the environments in which the various storms on this day evolved. The model was initialized horizontally-heterogeneously, using RUC (Rapid Update Cycle) analyses and surface observations. Topography was obtained from the United States Geological Service (USGS) 30-second datasets while vegetation type is based on the Biosphere-Atmosphere Transfer Scheme (BATS) of Dickinson et al. (1986). An API (Antecedent Precipitation Index) scheme was used to estimate the distribution of soil moisture. A simulation using three nested grids (horizontal grid spacings 60 km, 20 km, and 5 km) was performed, encompassing the Great Plains and surrounding states. On the 5 km grid, covering the eastern Texas Panhandle and extreme western Oklahoma, a number of convective 'events' occurred east of the model dryline and south of the cold front. The simulation was then repeated a number of times using a fourth nested grid (1 km grid spacing) at the location of a particular convective event in order to resolve more fully the morphology of the storms. Comparisons are performed with VORTEX proximity soundings and observed storm behavior. Environmental factors which could have lead to the differences in evolution of the storms are discussed, in addition to the capability of the model configuration to resolve the difference between tornadic supercells and supercell null cases.
Session 17, Severe storm numerical modeling
Saturday, 16 September 2000, 8:00 AM-9:43 AM
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