ABSTRACT

An unusual outbreak of severe thunderstorms over the desert and complex terrain of southern New Mexico and far west Texas occurred on 7 June 1997, with numerous instances of large hail, flash flooding, radar-indicated mesocyclones, and tornadoes reported. The Pennsylvania State University/National Center for Atmospheric Research Mesoscale Modeling System V (MM5) was used in an attempt to simulate observed mesoscale features of this day, with several runs of the model compared using different choices for cumulus parameterization. The MM5 was run in a triple nest configuration, at horizontal resolutions of 45, 15, and 5 km and with two-way feedback between meshes permitted. Results of the MM5 simulations were compared, examining how each of the numerical solutions were able to evolve the observed convection, along with other important synoptic and mesoscale features (such as dryline formation and propagation). Each of the MM5 simulations forecasted at least some aspect of the meteorology well, although all the simulations poorly resolved the dryline axis orientation and were too quick to mix out the low-level moisture in the western area of the grid. At 5 km grid resolution, many of the assumptions used in cumulus parameterization begin to lose validity, although the resolution is still too coarse for explicitly resolving individual convective plumes. Results of the simulations show that those simulations produced using any of the various cumulus parameterizations (on the 5 km inner nest), evolve the overall timing and location of the convection more realistically than the single simulation using explicit resolution on the inner nest.