Avalanche Forecast
Regions: Dogtooth, East Purcell, Esplanade, Purcells, St. Mary, West Purcell.
Avoid exposing yourself to avalanche terrain or overhead hazards on Saturday. Upper elevations are heating up and very large natural avalanches are expected.
Confidence
Moderate
Avalanche Summary
A few more natural, remote, and explosives-triggered persistent slabs were observed Thursday, failing on the same late-January crust that caught a skier in a size 1.5 in Golden Tuesday and gave natural size 3 and 3.5 releases in the Dogtooth Range on Wednesday.
Size 2 and 3 deep persistent slabs were explosives-triggered on Wednesday, showing the basal snowpack reacting to large triggers.
Activity of this type should resume or even intensify as warming continues.
Snowpack Summary
A melt-freeze crust moist or snow now glazes the surface on solar aspects and potentially to mountaintop by Saturday afternoon. High overnight freezing levels mean crust recovery may be weak. This process is affecting 20 to 45 cm of settling recent snow, which has been redistributed by strong southwest winds at treeline and above. In shelter, it sits over a surface hoar or crust layer from mid-February.
Two more weak layers exist: a layer of facets, surface hoar, or crust from late-Jan buried 30 to 50 cm deep, and a layer of facets from early Dec, buried 70 to 120 cm deep. In many areas, facets or depth hoar also exist at the base of the snowpack. All of these layers are a concern as warming tests the snowpack.
Weather Summary
Friday Night
Clearing. 0 to 5 km/h southwest ridgetop wind. Freezing level remaining near 1800 m.
Saturday
Sunny. 5 to 10 km/h southwest ridgetop wind, up to 30 km/h in alpine. Freezing level rising to 2600 m. Treeline temperature 4 °C.
Sunday
Mainly sunny with cloud increasing. 0 to 5 km/h variable ridgetop wind. Freezing level 2000 m - 2500 m. Treeline temperature 4 °C.
Monday
Clearing after overnight flurries and up to 5 cm of snow above about 1700 m. 10 km/h northeast ridgetop wind. Freezing level 1700 m. Treeline temperature around 0 °C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be aware of the potential for large, destructive avalanches due to deeply buried weak layers.
- Avoid thin areas like rocky outcrops where you're most likely to trigger avalanches on deep weak layers.
- Avoid exposure to overhead avalanche terrain; avalanches may run surprisingly far.
- The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
Avalanche Problems
Persistent Slabs
A trio of weak layers exist below the most recent storm snow and up to about 120 cm below the surface. They will be increasingly likely to produce avalanches during the warmup. Small avalanches may also step down to the basal snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1.5 - 3
Deep Persistent Slabs
Forecast warming is bringing the weak, faceted basal snowpack into question. As warming penetrates deeper into the snowpack, the chances of full-depth avalanches increase.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible - Likely
Expected Size: 2.5 - 3.5
Loose Wet
High freezing levels and solar warming will work to destabilize snow on steep slopes sheltered from the wind. Moist or wet snow may shed naturally or with a human trigger and loose releases may trigger more destructive slab avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 1.5