If you venture into the high country in search of soft snow, exercise caution around lingering pockets of wind slab formed by northerly winds, they may be poorly bonded to the crust below.
Last week's snowfall was accompanied by strong southwest winds, which then shifted to the northeast, forming wind slabs on a variety of aspects in exposed terrain in the alpine and treeline. These slabs may linger in isolated areas.
On Thursday a large (size 2) natural avalanche occurred in the alpine on a north aspect. This avalanche crown was 100 cm depth and is likely the early February persistent slab problem.
On Friday near Rogers Pass, there were a few natural storm slab avalanches (size 1-2) from extreme terrain in the highway corridor.
Looking forward to Sunday, the main concern will be the potential for small (size 1) wind slabs in alpine and treeline terrain.
Valley bottoms are generally snow-free. As you gain elevation below treeline, a shallow spring snowpack exists with a strong surface crust that softens with daytime warming.At treeline and above, 5 to 20 cm of wind-affected dry snow exists on a variable crust on all but high northerly aspects, which may still hold dry snow. We have a seasonally low snow depth of roughly 200 cm at treeline.Weak faceted grains above a crust formed in early February are now buried 100 to 150 cm deep. This layer is generally getting stronger, and in most places it is shielded by crusts above, but it is still occasionally producing large avalanches at upper elevations.
Saturday Night
Cloudy with clear periods and light flurries. Ridge wind 10 to 30 km/h from the southwest. Treeline temperature drops to -6 °C. Freezing level drops to 1000 m.
Sunday
A mix of sun and cloud with light flurries. Ridge wins 15 to 30 km/h from the southwest. Treeline temperatures reach a high of -3 °C. Freezing level rises to 1700 m.
Monday
Cloudy with precipitation increasing in the afternoon, 5 cm new snow accumulation at higher elevations. Ridge wind 30 to 50 km/h from the southwest. Treeline temperature -2 °C, freezing level 1500 m.
Tuesday
Cloudy with mixed precipitation, 5 to 15 cm of new snow accumulation at higher elevations. Ridge wind southwest 30 to 60 km/h. Treeline temperature -1 °C, freezing level 1700 m.
More details can be found in the Mountain Weather Forecast.
