The Snake River Plains Convergence Zone: dynamics, climatology, and predictability

The Snake River Plain Convergence Zone (SPCZ) is a post-frontal, terrain-channeled boundary-layer shear/convergence zone in the Snake River Plain of eastern Idaho (Andretta and Hazen 1998). It forms in the lee of the Central Idaho mountains, yet the downstream mountains in eastern Idaho are important as well.

This paper includes a modelling/observational case study of a significant snowfall event in eastern Idaho that occurred on 26 November 2005. The region of heavy snowfall was localized in the Lower Snake River Plain with amounts varying from between 10 and 15 inches east and south of the city of Pocatello, to between 1 and 4 inches near the Pocatello Regional Airport. This snowfall event was driven by two principal forcing mechanisms: (1) a mobile zone of orographic boundary layer convergence in the Snake River Plain which generated several moderate to heavy mesoscale snowbands in the lower plain and (2) a progressive zonally oriented low-level jet in the Magic Valley which aided in upslope flow and strong vertical motions near Pocatello and in the Pocatello Range. The study describes the high resolution operational WRF-ARW model grids consisting of outer (12 km), inner 1 (4 km), and inner 2 (1.33 km) domains. The paper also provides mesoscale analyses of satellite imagery, surface observations, radiosonde data, and aircraft soundings. It also features state-of-the-art GIS scenes of high resolution surface mesonet data and radar imagery captured at different stages of the event.