Avalanche Forecast
Regions: Dogtooth, East Purcell, Esplanade, Purcells, St. Mary, West Purcell.
Weak crust recovery and another day of dramatic warming should keep persistent slabs at their tipping point. Manage the high-consequence snowpack with low-consequence terrain.
Confidence
Moderate
Avalanche Summary
More natural, remote, and explosives-triggered persistent slabs were observed Thursday and Friday, failing on the same late-Jan crust that caught skiers in size 1.5 releases in Golden Tuesday and again Friday and gave natural size 3 and 3.5 releases Wednesday.
Size 2 - 3 deep persistent slabs were explosives-triggered Wednesday, showing the basal snowpack reacting to large triggers.
Heightened persistent slab activity will be concern for the duration of the warmup
Snowpack Summary
A melt-freeze crust or moist snow likely makes up the surface on all but high elevation north aspects. High overnight freezing levels mean crust recovery may be weak. This crust tops the upper part of 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
Saturday Night
Clear. 0 to 5 km/h southwest ridgetop wind, up to 30 km/h in alpine, easing. Freezing level peaking at 2800 m.
Sunday
Mainly sunny with cloud increasing in the afternoon. 0 to 5 km/h variable ridgetop wind shifting northeast. Freezing level 2400 m. Treeline temperature 3 °C.
Monday
Mainly cloudy with scattered flurries bringing 5 - 10 cm of new snow above about 1700 m. 10 to 15 km/h northeast ridgetop wind. Freezing level 1700 m. Treeline temperature around 0 °C.
Tuesday
Mainly sunny. 0 to 5 km/h southwest ridgetop wind, up to 30 km/h in alpine, increasing. 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 likely to produce avalanches throughout the warmup. Small avalanches may also step down to the basal snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: 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: South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1.5