Mesoscale Weather Effects of Variable Snow Cover over Northeast Colorado

Abstract

Data from the PROFS (Program for Regional Observing and Forecasting Services) surface mesonetwork have been used to document the effect of variable snow cover on atmospheric boundary layer properties cloudiness and weather conditions over north Colorado on 15 April 1983. On this day an oval-shaped ?104 km2 area of snow-free ground surrounded by snow-covered ground existed along the Colorado Front Range. While sky conditions on the morning of this day were everywhere clear, cloudiness developed by midday over the snow-free region as a result of the more rapid boundary-layer heating and mixed-layer growth there. During midafternoon snow showers occurred over the snow-free ground whereas sides remained mostly clear over the snow-covered area. Our analysis suggests that snow boundaries in the region may have acted through the development of a weak solenoidal field to enhance low-level inflow into the snow-free area, thereby assisting with cloud development in the region. Analogous to the sea bronze, this phenomenon might be termed a ?snow breeze?. Even without such an enhancement to the circulation, the variable snow cover through its impact on the surface energy budget had a profound effect on the regional weather conditions on that day. This situation represents just one example of a class of complex interactions and feedback processes involving variable surface properties and the large-scale flow.