11.6 A Modeling Investigation into the Dynamics and Microphysics of Low-Precipitation Supercells

Thursday, 8 August 2013: 11:45 AM
Multnomah (DoubleTree by Hilton Portland)
Leah D. Grant, Colorado State University, Fort Collins, CO; and S. C. van den Heever

The supercell spectrum, which represents a continuum of supercell types, is characterized by three main classes: low-precipitation (LP), classic, and high-precipitation (HP) supercells. While LP supercells pose severe-weather threats similar to classic and HP supercells, including large hail, lightning, and tornadoes, they are the most difficult of the supercell types to identify on radar. Consequently, observational studies of LPs are somewhat limited. Furthermore, very few modeling simulations of LPs have been reported in the literature. The physical processes leading to the differences in supercell morphology are therefore not well understood.

In this study, the question of whether dynamical and microphysical differences exist between supercell types, specifically between LP and classic supercells, as well as the mechanisms leading to their differing precipitation distributions, are explored through the use of cloud-resolving model simulations. A classic supercell and multiple LP supercells have been simulated with the Regional Atmospheric Modeling System (RAMS) using a horizontal resolution of 300 meters. Preliminary results indicate that LP supercells can form when an elevated dry layer is present in the environmental moisture profile, such as may be seen near the dryline or within environmental conditions unmodified by previous convection. Simulated LP features include reduced precipitation efficiencies relative to the classic supercell; a relative lack of precipitation within the rear-flank-downdraft region; and a narrower updraft, in general agreement with previous observational studies. Differences in storm dynamics and microphysics between classic and LP supercells, including cold pool characteristics, storm motion and thus storm-relative winds and helicity, as well as hail formation mechanisms, will be presented.

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