Application of the snow cover model SNOWPACK to snow avalanche warning in Niseko, Japan

We describe the use of the snow cover model SNOWPACK for avalanche warning in Niseko, Japan. Input data was collected from a newly installed meteorological station at 800 m a.s.l. To verify the model output, snow pit observations were made almost everyday during the winter 2002-2003. Ten dry snow slab avalanches occurred during the observation period. Most of them were released after a heavy storm and had fracture depths of 40-60 cm. Pit observations revealed that the fracture layers in the snowpack consisted of either graupel or stellar precipitation particles without rime (70%) or faceted crystals (30%). Slab layers consisted of precipitation or decomposing and fragmented particles, which indicated that these avalanches occurred soon after the snow deposition. Snow profiles simulated with SNOWPACK roughly agreed with the observed profiles. The model reproduced faceted crystals on a crust that became the weak layer and caused the avalanches on 14-16 February 2003. In addition, air temperature, solar radiation, wind speed, and snow depth in the study area were estimated for grid points with 50 m spacing. This allowed to calculate for each grid point snow properties such as grain type and density as well as the snow stability index SI. The predictions agreed reasonably well with the field observations.