Avalanche Forecast
Regions: Dogtooth, East Purcell, Purcells.
Human-triggered avalanches remain likely on weak layers buried deep in the snowpack. Avalanches occurring on these layers will be large with high consequences.
Check out the Forecasters blog for strategies to manage the persistent and deep persistent avalanches problem found in this area.
Confidence
Moderate
Avalanche Summary
A small rider-triggered avalanche was released on the persistent weak layer and explosive control continues to produce small avalanches failing on the deep persistent weak layer.
Reports of new human-triggered avalanches have started to taper. However, with little change in the snowpack structure, triggering large persistent slab avalanches remains a concern, especially in steep, shallow, rocky areas.
Snowpack Summary
Wind slabs are forming in lee terrain features from southerly wind in wind-exposed terrain. These new wind slabs sit on variable surfaces of soft snow in sheltered areas, a layer of surface hoar and/or crust.
The mid and lower snowpack is generally weak and faceted and continues to be a concern. Avalanche activity on these layers has tapered, however, the snowpack structure remains the same.
The two layers of concern are relatively close together, the upper weak layer developed in mid-December is 30 to 50 cm deep. The lower weak layer developed in mid-November 70 to 100 cm
Snowpack depths are roughly 60 to 160 cm at treeline. This year's snowpack is weaker than usual, as described in our Forecasters' blog.
Weather Summary
Friday Night
Clearing overnight, no new snow, 10 to 20 km/h southwest wind, treeline temperature -5 °C.
Saturday
Mostly clear skies with increasing clouds throughout the day, with trace amounts of snow. 10 - 20 km/h south wind, treeline temperatures -5 °C.
SundayMostly cloudy, 2 to 5 cm new snow, 10 - 20 km/h southwest winds decreasing through the day, treeline temperatures - 7 °C.
MondayPartly cloudy, trace of new snow, 15 to 20 km/h southwest winds, treeline temperatures -7 °C
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
- Choose conservative terrain and watch for clues of instability.
- Remote triggering is a concern, watch out for adjacent and overhead slopes.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Avalanche Problems
Persistent Slabs
A layer of surface hoar, facets and/or a crust may be found around 40 to 70 cm deep, which is a prime depth for human triggering. To date this layer has been most problematic around treeline and lower alpine elevations and has formed large avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 2 - 3
Deep Persistent Slabs
A layer of large and weak facets sits near the base of the snowpack. This layer has most recently been problematic in lower alpine elevations. Riders are most likely to trigger it in terrain with shallow, variable snow depths. Shallower avalanches could also step down to this layer, producing a very large and consequential avalanche.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 2.5 - 3.5
Wind Slabs
Southerly wind is forming new wind slabs in lee terrain features. Avalanches triggered in wind-loaded terrain have the potential to step down to deeper weak layers, creating larger than expected avalanches.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1.5