Northwest Coastal Avalanche Forecast

Issued: Feb 7th, 2021 4:00PM

Mon Feb 8th Current Conditions
Alpine Moderate Treeline Moderate Below Treeline Low
Tue Feb 9th 2 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Low
Wed Feb 10th 3 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Low

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

A weak layer of surface hoar lurks in sheltered features, dig down and investigate the bond between recent storm snow and the old surface. At upper elevations be wary of windslabs in loaded terrain.

Summary

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

SUNDAY NIGHT - Clear and cold / moderate to strong northwest wind / alpine low temperature -25

MONDAY - Mix of sun and cloud / light to moderate northwest wind / alpine high temperature near -18

TUESDAY - Mostly sunny / moderate northwest wind / alpine high temperature near -20

WEDNESDAY - Sunny / moderate increasing to strong northeast wind / alpine high temperature near -20

Avalanche Summary

On Saturday, a size 2 persistent slab avalanche was intentionally triggered on a north aspect at 1200 m, the crown was 35 cm. Skiers also reported a reactive weak layer down 35 cm producing cracking underfoot and sudden results in test profiles between 800 and 1100 m. In the far north, a handful of small (size 1.5) wind slab avalanches failed naturally.

On Friday, numerous dry loose avalanches were reported up to size 2 during the storm in steep terrain. 

On Thursday, reports indicated several small features were reactive up to size 1 on the surface hoar that was buried in late January. I suspect that once the persistent slab gains more cohesion and stiffens, this problem may become more widespread. Even a small avalanche can catch you by surprise and have enough mass to push you into a terrain trap below. 

Snowpack Summary

30-70 cm of recent storm snow from the past week covered on a persistent weak layer which consists of surface hoar in locations sheltered from the wind, and facets and stiff wind affected snow at upper elevations (upper treeline and the alpine). Winds are redistributing loose snow into slabs at upper elevations. At lower elevations, (lower treeline and below treeline), 10-30 cm of snow sits above isolated pockets of surface hoar and a crust that is more prominent on solar aspects. 

The mid-pack seems to be well settled. Deep persistent layers appear to have mostly become unreactive, with the exception of the Bear Pass area and the far reaches south of Kitimat. 

Terrain and Travel

  • 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.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible

Expected Size

1 - 2

20-40 cm of new storm snow has slowly accumulated over the past few days. Changing wind directions may deposit deeper and stiffer slabs on multiple aspects. I suspect that anywhere the new snow feels stiff and more cohesive the slab may be more reactive, especially where it sits above a buried weak layer. 

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

1 - 2

30-70 cm sits above a buried weak interface that consists of surface hoar, facets, and/ or a crust. As the snow above this layer becomes more consolidated, the likelihood of avalanches may increase.

Aspects:

All aspects.

Elevations:

Treeline, Below Treeline.

Valid until: Feb 8th, 2021 4:00PM

Forecast Trend

The latest forecast danger ratings, broken down to elevation. See how an elevation is trending.