The Simulated Impact of the Snow Albedo Feedback on the Rocky Mountain Front Range Mountain-Plain Circulation Under Climate Change

The Front Range mountain-plain circulation (FRMC) is a large-scale diurnally driven wind system that occurs east of the Colorado Rocky Mountains in the United States and affects the weather both over the Rocky Mountains and the adjacent Great Plains. As the climate warms, the snow albedo feedback (SAF) will amplify the warming response over the Rocky Mountains during the spring, increasing the thermal contrast between the mountains and plains, potentially modifying the strength and character of the FRMC.

In this study, we perform 7-year regional climate simulations using the Weather Research and Forecasting model (WRF) with a 12-km grid spacing. These include a reanalysis-forced control simulation, a pseudo global warming (PGW) climate change simulation, and an idealized “fixed albedo” PGW experiment designed to isolate the sensitivity of the FRMC to the SAF. We find a mean increase in the springtime FRMC strength during afternoon hours in the PGW experiment that is largely driven by increases in the temperatures contrast between boundary layer air over the mountains and plains caused by the SAF. Furthermore, inter-annual variability of changes in FRMC strength is strongly influenced by inter-annual variability in the SAF.

Additionally, we use WRF to preform a case study experiment with a finer 1.3 km grid spacing to examine the details of how the FRMC responds to the SAF. This experiment includes a passive tracer to investigate the impacts of FRMC changes on pollution transport. The case study reveals that loss of snow cover causes an increase in the strength of the FRMC and a corresponding increase in boundary layer concentrations of tracer transported from the western Great Plains over the Front Range Mountains