Measuring and Modelling a Major Winter Precipitation Event in the Canadian Rockies

English Abstract:

Mountains present extraordinary challenges to both snow measurement and modelling. The seasonal snowpack in the Canadian Rockies is strongly influenced by accumulation and redistribution during and after snowstorms. Often just a few large storm events determine the main characteristics of the seasonal mountain snowpack. Quantifying the temporal and spatial distribution of mountain snowpacks due to individual storms is therefore of great interest for water supply prediction from mountains. In order to assess the variability and uncertainty in accumulation and ablation associated with a major snow storm, precipitation, snow accumulation and snow depth measurements were made in the Canadian Rockies during and after a major storm event in November 2014. The storm was characterised by strong winds and rapidly decreasing air temperatures as a cold front advanced from the north. Measurements suggest that snowfall of up to 90 mm SWE over two days was caused by uplifting of a warm, relatively moist, air mass as the cold front advanced. Blowing snow, and potentially preferential deposition, contributed to the highly variable post-storm snow accumulation. To assess the relative contributions to variable snow accumulation, snowfall gauge undercatch corrections were applied to sites with different wind exposures but identical precipitation gauge types and compared to results from automatic and manual snow accumulation and snow depth measurements in sheltered and open sites. A blowing snow model was then run to estimate blowing snow redistribution. The results suggest that there is great uncertainty in estimating snowfall in this environments because gauge-undercatch corrections established at flat test sites do not produce credible values in complex terrain and because snowfall gauges bridge with large snowfall amounts. The relative impacts of measurement errors, preferential deposition and blowing snow redistribution are discussed.