Topographic Sensitivity of the Snake River Plain Convergence Zone of Eastern Idaho. Part II: Numerical Simulations

Abstract

The Snake River Plain Convergence Zone (SPCZ) is a mesoscale topographic weather system in the planetary boundary layer that occasionally forms in a post-cold-frontal environment during the cold season in eastern Idaho. Part I of this study investigated persistent and locally heavy topographic snowfall associated with such a zone on 26 November 2005. Multiple snowbands formed in the presence of conditional, convective, and inertial instabilities. In Part II, nested grid high-resolution numerical simulations of the WRF-ARW model are used to investigate the structure and evolution of the SPCZ with two different terrain grid scales. In a smoothed topography with a coarsely resolved tributary valley system upstream of the broad parabolic-shaped Snake Plain, the model does not simulate a lee convergence band and vorticity dipole. These features are evident in the observations and control simulation. The smoothed run also misses snowfall associated with windward convergence and stable upslope flow in the Pocatello-Inkom area. Nevertheless, both model runs depict topographically-generated convective storms and potential vorticity anomalies in the plain.