Snowpack model calculations for avalanche warning based upon a new network of weather and snow stations

Abstract

The Swiss Federal Institute for Snow and Avalanche Research (SLF) began to construct a network of high Alpine automated weather and snow measurement stations in the Summer of 1996. Presently, more than 50 stations are in operation. The stations measure wind, air temperature, relative humidity, snow depth, surface temperature, ground (soil) temperature, reflected short wave radiation and three temperatures within the snowpack. The measurements are transferred hourly to the SLF in Davos and the data are used to drive a finite-element based physical snowpack model. The model runs every hour and provides supplementary information regarding the state of the snowpack at the sites of the automatic stations. New snow amounts, settling rates, possible surface hoar formation, temperature and density profiles as well as the metamorphic development (grain types) of the snowpack are all predicted by the model. The model is based on a Lagrangian finite element implementation but solves the instationary heat transfer and settlement equations. It includes phase changes and transport of water vapor and liquid water. Special attention is given to the metamorphism of snow and its connection with the mechanical properties such as thermal conductivity and viscosity. The model is connected to a relational database that stores the measurements as well as the model results. New visualization tools are available which allow a fast, easy and comprehensive access to the stored data. The model has been tested in operational mode during the Winter of 1998/1999. The calculations is reliable in terms of the energy budget and the mass balance. The implemented snow metamorphism formulations yield reasonable grain types and are able to reproduce important processes such as formation of depth hoar. The results of the simulations are used by local, regional and national avalanche forecasters and provide valuable information on the snow conditions in the vicinity of avalanche starting zones during the catastrophic avalanche situation in February 1999.