Observed vertical structure of snow storms in Steamboat Springs, CO: Orographic enhancement in a high altitude environment

Ground-based radar profiles, in situ observations, and sounding data were collected as part of the Inhibition of Snowfall by Pollution Aerosol (ISPA) study centered at the Desert Research Institute's Storm Peak Laboratory (SPL) in Steamboat Springs, CO during January and February 2010. Observations include data from two vertically pointing Metek Microwave-Rain Radars (MMRs), an optical OTT Parsivel disdrometer, a GPS Advanced Upper-air Sounding (GAUS) system, a Radiometrics profiling microwave radiometer, and surface meteorology sensors. Observations were collected at SPL atop Mt. Werner, as well as in the valley near the town of Steamboat Springs. Twenty-two snowfall events were observed over the six week project.

Snowfall cases are separated into along-barrier, diagonal-barrier, and cross-barrier flow directions and quantitative statistics are computed. Intercomparisons between the valley and mountain top radar profiles of reflectivity and Doppler velocity are used to understand the nature of orographic enhancement and differences between valley and mountain snow events. Joint frequency distributions of reflectivity with height and Doppler velocity with height are used to elucidate differences in snow storm 3D structures over the mountain versus the valley and as a function of flow direction. Preliminary interrogation of cases reveals more precipitation enhancement during cross-barrier upslope flow compared to other flow directions. Upslope flow is seen to extend several km above mountain-top level in some cases.

Improving forecasts and better understanding the dynamics controlling snowfall are important because of the economic impact snow events have on the surrounding economy near Steamboat Springs. The findings of this study complement the overall context of ISPA, which aims to quantify the impacts pollution aerosols have on winter-season-long precipitation across the Colorado mountains and Colorado River basin. Snowfall data are used across disciplines--by hydrologists and agricultural specialists for water table and water resource concerns, as well as for avalanche hazard assessment.