Avalanche Forecast

Moderate - Forecast snowfall amounts are uncertain on Thursday

WEDNESDAY NIGHT: Mainly cloudy with flurries, accumulation of 5-10 cm, moderate southwest winds, alpine temperature -6 CTHURSDAY: Isolated flurries, moderate south winds, alpine temperature -3 C, freezing level 1200mFRIDAY: Cloudy with sunny periods, light southwest winds, alpine temperature -3 C, freezing level 1300 mSATURDAY: Mix of sun and cloud, light southwest winds, alpine temperature 1 C, possible temperature inversion

A size 3-3.5 persistent slab avalanche was skier triggered on the north side of the highway in Glacier National Park on Tuesday. This was triggered from a thin spot on the ridge at 2250 m on a south east aspect. It ran to the valley bottom and is suspected to have run on a layer of surface hoar sitting on a crust that was buried in late November. See the MIN post here. Although outside of the South Columbia region it is a notable avalanche that illustrates the potential for thin spot triggering of deeper weak layers that may be reactive in isolated areas in this region.

Snowfall combined with wind on Wednesday into Thursday will have formed new wind slabs in lee and cross-loaded terrain features at high elevations. This new snow has fallen on widespread wind-affected snow at alpine and treeline elevations. Below this, the snowpack is generally well-settled. There is however, a layer of feathery surface hoar that is sitting on a crust that was buried late November down 100-200 cm. This crust is suspected to be the bed surface for few notably large avalanches over the past 2-3 days on southwest through southeast aspects in the North and South Columbia regions.