Avalanche Forecast

Wednesday night: Clearing overnight, light northwest wind, alpine temperature -14 C.

Thursday: Mix of sun and cloud, light northwest wind, alpine high temperature -11 C.

Friday: Cloudy, scattered flurries with 1-3 cm of snow, light southwest wind, alpine high temperature -10 C.

Saturday: Cloudy, scattered flurries with 2-5 cm of snow, light southwest wind, alpine high temperature -8 C.

The majority of avalanches reported on Wednesday occurred where the wind played a role in stiffening slabs, particularly below ridge crests. These avalanches were small (size 1-1.5).

Prior to the storm, numerous human-triggered were reported releasing on weak layers formed in late December across aspects and elevations. Many of these avalanches were large (size 2-2.5), breaking 50-80 cm deep. Several of them have been remote-triggered, like this MIN from Saturday. Be sure to check out this MIN and this MIN for helpful reports of slopes that are likely to harbor this problem. 

Within the past week, explosive control work and other large triggers have produced large and very large (size 2-3.5) deep persistent slab avalanches on early season weak layers from November on all aspects in alpine terrain. One of these avalanches reportedly released naturally on Monday. Characteristics common to these avalanches include wide propagation and full depth avalanches scouring away the snowpack to ground. It is possible that easier-to-trigger storm slab avalanches could step down to these deeper, persistent layers.

The most recent storm delivered 15-35 cm of snow across the region with strong southwest winds. Expect storm slabs to be especially touchy in lee terrain features where winds have been drifting new snow into stiffer, more reactive slabs. Periods of sun possible on Thursday have the potential to promote instability in the storm snow on sun-affected slopes.

Two mid-pack surface hoar layers from mid to late December are now buried 70-130 cm deep. Snowpack tests and avalanche activity give evidence to this weak layer's potential to produce large, destructive avalanches.

The base of the snowpack in the Purcells is much weaker than in an average season, and there are deeper weak layers down 120 to 200 cm. This weakness is widespread across all aspects and elevations, and it consists of crust, facets and depth hoar. It remains possible to trigger these deep weak layers in areas where the snowpack is thin, rocky, or variable.

• Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.
• Conditions may have improved, but be mindful that deep instabilities are still present.
• Brief periods of sun could quickly initiate natural avalanche activity.