Heavy Snowfall Produced by Topographically-Induced Winds in the Snake River Plain of Eastern Idaho. Part I: Observational Analysis

Abstract

This study is the first of two papers concerning the dynamics of a heavy snowfall event in the Snake River Plain of eastern Idaho on 26 November 2005. Heavy snowfall occurred along the southern perimeter of the wide (~100 km) valley and in three to four mesoscale bands aligned across the valley and parallel with the post cold-frontal northwesterly flow. This event was driven by two main topographic forcing mechanisms. First, widespread precipitation resulted from a low-level barrier jet (oriented down a tight horizontal pressure gradient) ascending the Snake River Valley and spilling over the southern edge of the valley. Second, the mesoscale snow bands in the valley resulted from boundary layer convergence forced by flow through the upstream barrier, the Idaho Central Mountains, in three narrow valleys aligned with the 700 hPa wind. This case study illustrates how the unique topography of eastern Idaho contributed to near-blizzard conditions in a post-frontal regime.