Avalanche Forecast
Regions: Purcells.
Concern remains for the weak layer that exists near the base of the snowpack. Deep persistent weak layers can be very difficult to manage, so a conservative approach to terrain is recommended.
Confidence
Moderate - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.
Weather Forecast
MONDAY NIGHT - Mainly cloudy with isolated flurries / southeast wind, 20-40 km/h / alpine low temperature near -8
TUESDAY - Cloudy with sunny periods and isolated flurries / southwest wind, 20-30 km/h / alpine high temperature near -6 / freezing level 1300 m
WEDNESDAY - Cloudy sunny periods and isolated flurries / southwest wind, 25-50 km/h / alpine high temperature near 75 / freezing level 1300 m
THURSDAY - Cloudy with sunny periods / southwest wind, 10-25 km/h / alpine high temperature near -6 / freezing level 1100 m
Avalanche Summary
On Sunday there were three deep persistent slab avalanches reported in the region. Two were triggered by explosives, but one that occurred near Golden was remotely triggered by humans. This activity outlines the fact that this layer remains a problem in the region. Large alpine features, especially rocky, thin snowpack areas are the most likely places to trigger this layer.
Since Thursday, there have been a few reports everyday of natural, human and explosives triggered storm slab and wind slab avalanches up to size 3, but mostly around size 2. These have occurred on all aspects, mainly at treeline and alpine elevations. The peak of this activity occurred on Saturday and has been tapering since. Wind loaded areas at treeline and in the alpine remain the most likely places to trigger an avalanche.
Snowpack Summary
The past week brought around 15-30 cm of snow to the region, with highest amounts in the south and west of the region. Strong southwest winds and warm temperatures have promoted slab development. Below about 1500 m the snow surface may exist as either a melt-freeze crust, or wet snow.
A weak layer of surface hoar can be found about 70 cm deep around Golden and Kimberley, 30 cm deep around Invermere, and 100 cm deep along Kootenay Lake.
As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall or explosives.
Terrain and Travel
- Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
- Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.
- Conditions may have improved, but be mindful that deep instabilities are still present.
Avalanche Problems
Wind Slabs
Wind slabs will likely be the most reactive in lee terrain features at upper elevations.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2
Deep Persistent Slabs
Triggering deep persistent slab avalanches is a relatively low likelihood but high consequence problem that is most likely in shallow, rocky start zones. Smaller wind slab avalanches could step down to this deeper layer, resulting in a very large avalanche.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely - Possible
Expected Size: 2 - 3