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Avalanche Forecast

Archived

Feb 7th, 2021–Feb 8th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Coastal.

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.

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

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.