Assessment of Mountain Snow Transport Based on Measured Wind and Simulated Snow Cover

A local to regional assessment of transported snow during snow storms or subsequent periods of strong winds is a prerequisite to reliably predict avalanche danger. Despite the fact that it has received continuing attention for decades, the problem of quantifying snow transport persists. Systems from point measurements to full three-dimensional simulations are in operation but all have their respective weaknesses. We present a new drift index, which has been tested and operated with some success in Switzerland. The index requires input from a windsheltered automatic weather station and an additional wind measurement at a wind-exposed site. Using the snow cover model SNOWPACK, the meteorological data is extrapolated to the four main expositions and snow cover development is calculated for these expositions. Depending on the measured wind direction and speed, a threshold condition for snow erosion at the upwind exposition is tested: if the wind is strong enough to erode the current snow at the surface of this exposition, the snow layer is eroded, transported and deposited onto the downwind exposition. With this scheme, the virtual, “representative” snow cover on the four main expositions in the vicinity of the meteorological stations are reconstructed for the course of the winter. Drifting snow periods are reasonably well detected and a quantitative information on snow deposition in lee slopes is possible. Compared to earlier versions of the index, which had been based on flat field simulations of SNOWPACK, the new index no longer overestimates intensity and duration of blowing snow events.