Cold air damming impacts on snowfall distribution along the eastern Wind River Mountains

The eastern slope of the Wind River Mountains (3500-4000m MSL) in central Wyoming is a favored location for upslope snow with northeast low-level flow that develops in the wake of cold frontal passages. Snowfall in the adjacent Wind River Basin and lower foothills shows a marked increase in amounts from Riverton to Lander. Local forecasters are adept at adjusting snowfall forecasts to account for this increase across the basin and into the adjacent east slopes of the mountain range. More interesting, however, are those snow events where locations in the lower foothills around Lander (1700-2100m MSL) receive snowfall exceeding that of mountain sites between 2600 and 3000m MSL.

Upper air soundings regularly show a stable lower atmosphere as cold air, often of Canadian origin, invades the Wind River Basin. Temperatures within this cold dome may not vary much since the air spills into the basin with higher terrain on all sides trapping the cold air. Within this cold, stable airmass, boundary layer wind observations indicate northeast upslope flow typically decelerates near Lander, either becoming near calm or light from the northwest parallel to the Wind River Mountains. While this deceleration can be partly ascribed to local mesoscale terrain features, local meteorologists have long theorized that cold air damming is occurring. A review of several cases will attempt to answer the question of, “Is cold air damming, and possibly a barrier jet, the likely determinant of heavy snowfall distribution in Lander and the lower foothills?”