Avalanche Forecast
Issued: Feb 7th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
cgarritty,
Avalanche Canada
Watch for fresh wind slabs in leeward terrain features on Saturday. Be prepared to take an extra step back if you find overnight snowfall has exceeded forecast amounts.
Summary
Confidence
Weather Forecast
Friday night: Cloudy with flurries bringing 5-15 cm of new snow. Light southwest winds, becoming strong at ridgetop before shifting northwest. Alpine high temperatures around -10.
Saturday: Cloudy with continuing light flurries bringing up to 5 cm of new snow. Light northwest winds shifting northeast. Alpine high temperatures around -10.
Sunday: Mainly sunny. Light west winds, becoming moderate or strong at ridgetop. Alpine high temperatures around -9.
Monday: Mainly sunny. Light west winds. Alpine high temperatures around -8.
Avalanche Summary
Explosives control in the central part of the region on Thursday successfully targeted several cornices and wind slabs with a mix of small and large results (size 1-2.5). A couple of remotely triggered cornice falls were observed during the work, as well as one recent natural cornice fall that triggered a slab on the reloaded bed surface of a previous deep persistent slab avalanche.
Since the weekend storm, there were several reports of failing cornices and small wind slabs. See this MIN report for a helpful illustration. Explosive control also released several large avalanches breaking on deeply buried weak layers on a variety of aspects above 2200 m. This activity is a good reminder that this layer remains a problem in the region. Easier-to-trigger wind slab avalanches or cornice fall may have the potential to step-down to this layer.
Snowpack Summary
20-40 cm of snow from the early part of the week now overlies older wind-affected snow at high elevations, or over a widespread melt-freeze or rain crust with a variable upper extent of 1800-2000 metres in elevation. The recent snow has mainly shown reactivity where winds have had a chance to redistribute it into new slabs. A few reports from adjacent regions have shown poor bonding with the buried crust where it exists.
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. Recent reports from the Golden area suggest a positive stabilizing trend. At lower elevations this layer has likely been bridged over by the above-mentioned crust.
As usual for the Purcells, the base of the snowpack contains basal facets. It remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall. Given this layer is most prominent in the alpine, it is unlikely to be effectively bridged over by our most recent crust.
Terrain and Travel
- Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Problems
Wind Slabs
Light snowfall overnight will combine with elevated and shifting winds to build new wind slabs that will need to be managed on Saturday. Be mindful of areas where wind slab and cornice distribution overlap.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A layer of weak, sugary facets persists at the bottom of the snowpack at higher elevations. Steep, rocky alpine features where the snowpack transitions from thick to thin are the likely trigger points for this deep persistent slab problem. Easier-to-trigger wind slab avalanches or cornice falls could step down to this layer, resulting in very large and destructive avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 8th, 2020 5:00PM
