63 Trends in Thermodynamic Instability and Vertical Wind Shear Variables with Increased Duration of Model Simulations

Thursday, 8 August 2013
Holladay-Halsey (DoubleTree by Hilton Portland)
Chad M. Shafer, Univ. of South Alabama, Mobile, AL; and N. R. Bramel, M. J. Brown, W. Clark, A. N. Kabeiseman, W. R. Schick, and M. W. Stanford

During a recent study of model simulations of severe weather outbreaks, a noticeable decrease in convective available potential energy (CAPE) was observed in simulations of increased forecast length. To determine if these results generalize to a larger sample of severe weather events and to identify other severe weather diagnostic variables exhibiting similar trends, a set of 100 severe weather outbreaks of varying intensity is selected, in which 1-, 3-, 5-, and 7-day WRF simulations are completed for each case. Several thermodynamic variables (CAPE, convective inhibition, the lifted condensation level, the level of free convection, etc.), storm-relative helicity of varying depth, and bulk wind differences of varying depth are evaluated and compared to analyzed data to quantify any observed trends. Additionally, four-week simulations during the warm season are conducted at preselected dates for a ten-year period to determine if these sensitivities are observed in a wide variety of environments. Preliminary findings suggest that WRF simulations do exhibit a decreasing CAPE trend over time for a wide variety of environments and for various model physical parameterization schemes, whereas the trends in the magnitudes of vertical wind shear variables are less susceptible to forecast duration.
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