Avalanche Forecast

Issued: Dec 6th, 2017 4:28PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is low. Known problems include Wind Slabs, Loose Wet and Deep Persistent Slabs.

cgarritty, Avalanche Canada

Northwest Inland.

Warm, sunny conditions are increasing the range of avalanche problems as well as their potential for reactivity.

Summary

Confidence

Moderate -

Weather Forecast

Thursday: Sunny with lingering valley cloud due to an alpine temperature inversion. Light southwest winds. Freezing level to 3200 metres with alpine temperatures around +5. Cooler at lower elevations.Friday: A mix of sun and cloud with cloud increasing over the day. Moderate to strong southwest winds. Freezing level dropping to about 2000 metres as the temperature inversion breaks down. Alpine temperatures around 0.Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Light to moderate southwest winds. Freezing level to about 1700 metres with alpine temperatures around -1.

Avalanche Summary

No recent avalanche activity has been reported, however stiff wind slabs now exist at treeline and in the alpine on leeward slopes and cross-loaded features. If triggered, these could step down to deeper weak layers and initiate large avalanches. The last significant avalanche observation was submitted on November 28th from Skilokis Creek. Here, a size 2.5 persistent slab was triggered from 150 m away. The possibility for further persistent slab activity will be elevated while temperatures remain unseasonably warm.

Snowpack Summary

Average snowpack depths now total 80-140 cm at treeline elevations and up to 160 cm in the alpine. (Depths of up to 210 cm have been reported from the Howsons.) Wind effect from recent strong southwest to northwest winds penetrated down into treeline elevations and resulted in fairly extensive wind slab formation. Below the wind-affected surface, approximately 30-50 cm of recent snow now overlies two crusts that were buried near the end of November. These crusts are widespread and extend into the alpine. Although recent snowpack tests have shown hard results at these crust interfaces, observations have been limited. Below these crusts, a well settled midpack overlies the late October crust near the base of the snowpack. This "crust/facet combo" is widespread and has been reactive to rider and remote triggers.

Problems

Wind Slabs

Recent variable winds mean that wind slabs can now likely be found on a wide range of aspects. Thursday's sun and warm temperatures will promote natural releases from steep terrain and may make slabs more reactive to rider triggers.

If triggered, wind slabs may step down to deeper layers and result in large avalanches.Avoid steep convexities and areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Loose Wet

Warm, sun-exposed slopes could produce wet loose avalanches either naturally or with rider triggers on Thursday, especially in steeper terrain.

Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

The late October crust lies near the base of the snowpack with a thin layer of weak, sugary snow above it. This layer has already produced very large avalanches with both rider and remote triggers.

Minimize or avoid exposure to overhead hazard.Be especially cautious in shallow snowpack areas where triggering a deeper layer may be easier.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Dec 7th, 2017 2:00PM