A Simulation of a Squall Line Using a Nonhydrostatic Cloud Model with a 5-km Horizontal Grid

Abstract

A three-dimensional nonhydrostatic cloud model is used to simulate the squall line observed in central Texas on 11 April 1979. The cloud model covers an area 400 ? 400 km2 with a 5-km horizontal resolution and is supplied initial and boundary conditions by a larger hydrostatic mesoscale model. The model produces a back-building squall line ahead of the surface cold front, as would be expected based on an analysis of the pre-squall-line environment. A well-defined gust front and cold pool develop with the squall line. At the end of the 5-h simulation, deep convection is found along a line nearly 400 km long. The simulated squall line compares favorably both with observations and with a higher-resolution model simulation in an environment of similar shear, suggesting that the 5-km horizontal resolution is adequately representing the significant features of the squall line. The major shortcoming of this study is the failure of the cloud model to produce the observed squall line at the proper time. Without the observed small-scale forcing, which was unresolved in the Severe Environmental Storms and Mesoscale Experiment (SESAME) dataset, the model is unable to generate the squall line until a larger-scale convergence area evolves, some 2?3 h after the appearance of the observed squall line.