From the Clouds to the Ground - Snow Precipitation Patterns in Complex Terrain

Snow accumulation patterns are determined by many different processes from ice crystal nucleation in clouds to snow redistribution by wind and avalanches. In between, snow precipitation undergoes different dynamical and microphysical processes, such as ice crystal growth, aggregation and riming, which determine the growth of particles and thereby influence the intensity and structure of the snowfall event. In alpine terrain the interaction of different processes and the topography may lead to orographic enhancement and preferential deposition of precipitation. To better understand the relative importance of different pre-depositional processes on snow precipitation we analyze three snowfall events between January and March 2016 in Davos (CH). Snow precipitation patterns from MeteoSwiss operational weather radar measurements on Weissfluhgipfel and very high resolution Weather Research and Forecasting (WRF) model simulations show reasonable agreement with measurements from automatic weather stations. Overall, radar precipitation patterns show higher small scale variability compared to WRF simulations. Two-dimensional autocorrelation maps and variograms of precipitation patterns reveal a strong dependence of radar and WRF precipitation on topography and the prevailing wind direction, which emphasizes the importance of large-scale orographic enhancement on regional scales and small-scale topography-wind interactions on a mountain ridge scale.