NUMERICAL-SIMULATION OF A LOW-PRECIPITATION SUPERCELL THUNDERSTORM

Numerical simulations of thunderstorms using initial conditions from an Oklahoma storm event on 26 April 1984 have been carried out using the Klemp-Wilhelmson cloud model. Two thermodynamic and two horizontal wind profiles are mixed to create four initial storm environments. The two initial thermodynamic profiles are designated as moderately and highly unstable. Both hodographs have considerable vertical wind shear, with the extremely unstable profile having substantially stronger storm-relative curvature shear in the lowest few kilometers, as measured by the helicity of the environment. Storms are initialized with two different temperature-perturbation warm bubbles. A variety of storms, qualitatively covering the range observed on this day, are simulated. With a strongly sheared, moderate instability environment, the two different temperature-perturbation simulations differ qualitatively, unlike the other pairs of simulations. Of particular interest is the simulation carried out with the weaker temperature perturbation. It displays many of the characteristics of observed low-precipitation (LP) supercell storms. Without artificially suppressing rainfall, this storm produces very little precipitation over the first 6000 s of its lifetime. During this time, there is no strong downdraft at the lowest model level and vorticity at that level is much less than the values aloft. We hypothesize that LP storms can be generated by smaller initial impulses than "classic" supercells in environments typically associated with a supercell storm, as speculated by Bluestein and Parks (1983), since they are more susceptible to turbulent entrainment in highly sheared environments.