Avalanche Forecast
Issued: Jan 18th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs.
jleblanc,
Avalanche Canada
Be mindful of a deep persistent slab problem, which is very difficult to forecast. Use caution on shallow snowpack areas and thin to thick steep rocky zones.
Summary
Confidence
Weather Forecast
TUESDAY NIGHT: Cloudy, light northwest wind, treeline temperatures around -3 C, freezing level lowering at valley bottom.
WEDNESDAY: Cloudy with sunny periods, light northwest wind, treeline temperatures around -6 C, freezing level at valley bottom.
THURSDAY: Snow 10-15 cm, moderate southwest wind, treeline temperatures around -5 C, freezing level rising to 1000 m.
FRIDAY: Mainly sunny, moderate northwest wind, treeline temperatures around -4 C, freezing level rising to 1000 m.
Avalanche Summary
No new avalanches were reported in the last 24h.
During the warm previous storm, mid-last week, a large widespread avalanche cycle occurred with most avalanches releasing within the storm snow and some on Jan 11 surface hoar layer. Strong solar radiation and warm temperatures were also at play after the storm, producing numerous avalanches at all elevations and scouring avalanche paths to the ground in places.
We have not heard reports of persistent slab avalanches for the last 10 days, when we saw numerous sizes 2 to 3 avalanches releasing on the early December facet/crust layer. Although the activity on this layer has tapered off, it still remains a concern as it is extremely difficult to forecast.
Snowpack Summary
Strong winds have redistributed the dry alpine snow, leaving variable wind slabs on specific terrain features. Around 1900 m and below, a crust is now capping the dense 10-30 cm of dense snow which has settled significantly with the past mild temperatures. The crust varies from thin/breakable to thick/supportive, according to the aspects and elevation. Below the recent snow, a layer of feathery surface hoar and melt-freeze crusts are found with decreasing reactivity. Lower elevations have gone through a melt-freeze cycle with past freezing level up to 1500m.
The early December crust/facet layer has been responsible for sporadic but very large, persistent slab avalanches over the past month. The crust is now buried 120-200 cm deep except in thin, wind-affected areas near ridgetops where most of the recent avalanches have been triggered.
Terrain and Travel
- Conditions may have improved, but be mindful that deep instabilities are still present.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Deep Persistent Slabs
A deep persistent slab problem formed by a crust down 140-200 cm has created a low likelihood, high consequence scenario that is difficult to forecast. This old and deeply buried weak layer is one of the most challenging problems to predict and for people to safely manage in the backcountry.
Although it hasn't shown recent activity, this problem is most likely to be triggered from thin or variable snowpack depth on wind-affected features, ridge crests, and near rocky outcroppings. The same feature or path can slide repeatedly when the persistent weak layer is reloaded with recent snow.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 19th, 2022 4:00PM
