Numerical Simulation of the Meso-β Scale Structure and Evolution of the 1977 Johnstown Flood. Part I: Model Description and Verification

Abstract

Abstract The Pennsylvania State University/NCAR mesoscale model, originally developed by Anthes and Warner, is modified to simulate the meso-β scale structure and evolution of convectively driven weather systems. The modifications include: (i) two-way interactive nested-grid procedures, (ii) the Fritsch-Chappell convective parameterization scheme, and (iii) the Blackadar boundary layer package. An 18-h simulation of the Johnstown flood of July 1977 is conducted. Compared to the documentation of Hoxit et al. and Bosart and Sanders, the simulation reproduced many of the different aspect of the mesoscale convective complex and squall line that were responsible for the heavy rain over western Pennsylvania. In particular, the model predicts the size, propagation rate and orientation of the mesoscale convective components that were observed in the mid-Atlantic states. The simulated evolution of the planetary boundary layer, cool outflow boundaries and surface pressure perturbations, such as meso-β scale lows, h...