Avalanche Forecast

Issued: Feb 3rd, 2021 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

Avalanche Canada swerner, Avalanche Canada

New snow, strong wind, and warming temperatures may add cohesion to the upper snowpack creating a stiffer slab and potentially stressing weak layers buried 30-70 cm down. This avalanche problem is less obvious and harder to predict, so conservative terrain choices are best.

Summary

Confidence

Low - Forecast snowfall amounts are uncertain. Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.

Weather Forecast

Wednesday Night: Snow amounts 5-15 cm. Alpine temperatures near -5 and freezing levels 400 m. Ridgetop wind 20-50 km/hr from the southwest.

Thursday: Cloudy with light snow 5-10 cm. Alpine temperatures near -1 and freezing levels near 900 m. Ridgetop wind light-moderate from the West.

Friday/ Saturday: Mix of sun and cloud. Alpine temperatures near -9 and freezing levels at the valley bottom. Generally light but gusty winds from the west-northwest.

 

Avalanche Summary

No new natural avalanche activity reported by Wednesday afternoon by 4 pm. Earlier this week, explosive triggered loose dry avalanches up to size 2 were reported from steep below treeline terrain. Additionally, some older (past 24-48hr) natural glide slab releases up to size 2 were spotted. In the far southern part of the region on Mt. Alexandra, an old (past 72hr) natural deep persistent avalanche release was reported size 3 from a NE aspect at 1700 m. 

The strong wind, rising freezing levels and new snow forecast for Thursday is driving the danger ratings to considerable. I suspect new wind slabs and storm slabs will be touchy. Especially where they sit above surface hoar, crust, or old surface facets. 

Snowpack Summary

Up to 15 cm of recent snow fell by Wednesday bringing 30-70 cm of accumulative storm snow from the past week over a variety of older snow surfaces. These old surfaces, at upper elevations (upper treeline and the alpine), include surface hoar in locations sheltered from the wind, surface facets, and stiff wind affected snow. At lower elevations (lower treeline and below treeline) 10-20 cm of snow sits above isolated pockets of surface hoar and a crust that is more predominant on solar aspects. Strong winds have stiffened the surface snow and have formed reactive wind slabs, especially in areas where they sit above the buried surface hoar. This recent MIN report is a great example of that. Additional snow and wind combined with cohesion may stress these potentially weak interfaces, creating the persistent slab problem.

The mid-pack seems to be well settled. Deep persistent layers appear to have mostly gone inactive with the exception of the Bear Pass area and the far reaches south of Kitimat that have seen some sporadic avalanche activity on weak snow near the base of the snowpack and triggered by large loads such as explosives, icefalls or cornice collapses.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Watch your sluff: it may run faster and further than you expect.

Problems

Wind Slabs

An icon showing Wind Slabs

Moderate southwesterly wind continues to redistribute the new snow and build fresh wind slabs in lee terrain features in the alpine and exposed treeline. Wind slabs will be particularly reactive anywhere snow overlies buried surface hoar or crust. The surface hoar layer is likely preserved in sheltered areas at and below treeline. In steep and wind-protected areas loose dry snow avalanches (sluffs) are expected. 

Large, looming cornices exist along ridgelines. Give them a wide berth from above and below.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

30-70 cm sits above a buried weak interface that consists of surface hoar, facets, and/ or a crust. Forecast snow and strong wind will likely add cohesion and load to these weak layers resulting in a reactive persistent slab problem.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1.5 - 2.5

Valid until: Feb 4th, 2021 4:00PM