Avalanche Forecast
Issued: Jan 13th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
cgarritty,
Avalanche Canada
Ease into terrain cautiously on Thursday. Start small and tune in to signs of instability like shooting cracks and recent avalanches. Be mindful that sunshine can have a powerful effect on stability - and on your desire to push into aggressive terrain.
Summary
Confidence
Weather Forecast
Wednesday night: Easing flurries bringing a final trace to 5 cm of new snow. Light to moderate northwest winds.
Thursday: Mainly sunny. Light variable winds. Alpine high temperatures around -8.
Friday: Cloudy with scattered flurries bringing up to 5 cm of new snow. Light south winds shifting west. Alpine high temperatures around -7.
Saturday: Mainly cloudy. Light variable winds. Alpine high temperatures around -7.
Avalanche Summary
A few preliminary observations from the aftermath of Tuesday's storm validated expectations of a busy day for natural avalanches. One natural size 2.5 (large) storm slab was observed in a lower elevation cutblock that had been crossloaded by strong winds.
In the Trans-Canada corridor, a size 4 (VERY LARGE) avalanche ran on Mt. Laurie. A few other size 1 and size 2 releases, both natural and skier triggered, were observed in the Galena Pass and Meadow creek areas. Observations were limited in some cases by strong winds.
Looking forward, expect Thursday to be another tricky day to be in the mountains, with new and reactive wind slabs formed in wind-exposed areas and even more widespread storm slabs primed for human triggering in more sheltered areas.
Snowpack Summary
30-40 cm of new snow fell during Tuesday's storm. The new snow buried wind affected surfaces at upper elevations, as well as surface hoar in wind sheltered areas and a thin crust on solar aspects.
The new snow will take time to form a bond with these previous surfaces, particularly in spots harbouring surface hoar or crust. In exposed areas, elevated winds are almost certainly redistributing new snow into reactive wind slabs and adding to cornices.
A couple of persistent weak layers exist in the upper to mid snowpack:
- The upper layer, now found an estimated 70-120 cm deep, is a spotty layer of surface hoar at treeline and below.
- The lower layer, now likely closer to 120-190 cm deep, is widespread and may present as decomposing surface hoar and/or a crust.
Avalanche activity on these layers has been dwindling since last week and snowpack tests results have generally indicated the weak layers are gaining strength. Given their age (particularly the deeper layer) and the testing load brought by Tuesday's storm, the outlook is good for these layers to finally become dormant as our current surface instabilities diminish.
Terrain and Travel
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Avoid exposure to steep sun exposed slopes.
Problems
Storm Slabs
New snow and strong winds have created new slab problems that are likely to vary with elevation and wind exposure. In exposed areas, thick and reactive wind slabs should be expected in leeward features loaded by the wind. In sheltered areas, storm slabs are more likely to exist uniformly across all aspects and be particularly touchy where they overlie surface hoar or crust.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A couple of weak layers exist in the mid snowpack, buried 70-120 cm and 110-190 cm below the surface. They are highly variable in distribution and trending toward dormancy, but they are being tested by a new load of new snow. Some potential currently exists for avalanches in surface layers to step down to a deeper layer to create larger, much more destructive avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 14th, 2021 4:00PM
