Item: An Operational Supporting Tool for Assessing Wet-Snow Avalanche Danger
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Title: An Operational Supporting Tool for Assessing Wet-Snow Avalanche Danger
Proceedings: International Snow Science Workshop Grenoble – Chamonix Mont-Blanc - October 07-11, 2013
Authors:
- Christoph Mitterer [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Frank Techel [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Charles Fierz [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Jürg Schweizer [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
Date: 2013-10-07
Abstract: Assessing the danger due to wet-snow avalanches is notoriously difficult, in particular, since conditions favouring wet-snow avalanches may persist only for a short period of time. The processes leading to wet-snow instability are complex and the response to them is complicated by fast, concurrently occurring changes in snow stratigraphy. In addition, liquid water does not penetrate snow uniformly. Already small changes in liquid water content will affect wet-snow stability. Previous studies have shown that knowledge of energy input combined with the cold content of the snowpack is important and useful to forecast wet-snow avalanches. Based on these studies we suggest an index defined as the average liquid water content of the entire snowpack, normalised by the starting value of the transition from the pendular to the funicular regime, i.e. 3% by volume. With the 1-D snow cover model SNOWPACK we calculated the index for virtual 38° steep south-facing slopes using meteorological data from 105 Automated Weather Stations (AWS) covering the Swiss Alps. We subsequently compared the index with wet-snow avalanche activity and regional danger estimates. During the 2011-12 and 2012-13 winters the index agreed well with observed wet-snow avalanche activity. It indicated spatial, i.e. elevation bands, and temporal patterns of wet-snow avalanche activity. Only for rain-on-snow induced wet-snow avalanches the forecast performance was poor since the AWS do not reliably measure liquid precipitation during wintertime and therefore we lack information on the transition from solid to liquid precipitation. Consequently, the snow cover model was not able to correctly simulate the transition from rain to snowfall (and vice versa). The results are promising and should improve the reliability of wet-snow avalanche forecasts. In addition, our approach allows a real forecast if output data of Numerical Weather Prediction models is used as input for the snow cover model.
Object ID: ISSW13_paper_P1-28.pdf
Language of Article: English
Presenter(s): Unknown
Keywords: wet-snow avalanches, forecast, energy balance, avalanche danger assessment
Page Number(s): 334-338
Subjects: avalanche forecasting avalanche danger wet snow avalanches
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