Avalanche Forecast
Regions: Purcells.
While refrozen surfaces at lower elevations pose little avalanche hazard, large avalanches may be triggered in areas with wind-drifted new snow at higher elevations. Be prepared to assess conditions and adjust your travel as you gain elevation.
Confidence
Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.
Weather Forecast
Saturday night: Decreasing cloud, scattered flurries with 2-5 cm of snow, moderate west winds, alpine temperature -10 C.
Sunday: Mostly clear, light northwest winds, alpine high temperature -8 C.
Monday: Partly cloudy, isolated flurries with trace accumulations, light northwest winds, alpine high temperatures -8 C.
Tuesday: Increasing cloud, light southwest wind, alpine high temperature -8 C.
Avalanche Summary
During the storm, numerous large (size 2-2.5) storm slab avalanches were reported in the region. They released naturally as well as from human and explosive triggers. These avalanches occurred on all aspects, mainly at treeline and alpine elevations. Reports indicate that cornices may be reaching their breaking point and may act as triggers for these avalanches. Below tree line, small wet loose avalanches were releasing naturally on Saturday.Â
Over the past week, there have been several deep persistent slab avalanches reported in the region. Two were triggered by explosives and 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. Easier-to-trigger storm slab avalanches or cornice fall may have the potential to step-down to this layer.
Snowpack Summary
30-50 cm of storm snow has accumulated at upper elevations (generally above 1900 m). Higher snow totals fell in the northern and western parts of the region. Strong southwest winds have drifted the snow into deeper, stiffer slabs in wind-exposed areas and have rapidly loaded cornices. During a warming event Saturday night, rain saturated snow surfaces up to around 1900 m that have since refrozen with cooling temperatures.
A weak layer of surface hoar may still be found about 90 cm deep around Golden and Kimberley, 50 cm deep around Invermere, and 130 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. New snow, rain, and warming will collectively add considerable strain to these weak layers. Their potential to fail naturally and produce large, destructive avalanches will be significantly increased during the storm.
Terrain and Travel
- Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Remember that the snowpack will be significantly different at higher elevations than lower down.
- When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
- If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
Avalanche Problems
Wind Slabs
Extreme winds from the southwest have drifted the storm snow into stiff slabs in wind-exposed areas that may be prone to human-triggering. This wind slab problem overlaps with areas where cornices have been rapidly loaded and could also act as triggers.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2.5
Deep Persistent Slabs
Rapid snowfall, ongoing wind transport, and fluctuating temperatures are testing the weak snow buried at the bottom of the snowpack. Triggering deep persistent slab avalanches is more likely in snowpack areas that transition from thick to thin, like in shallow, rocky start zones. Easier-to-trigger storm slab avalanches or cornice falls could step down to this deeper layer, resulting in a very large avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely - Possible
Expected Size: 2 - 3.5