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Avalanche Forecast

Archived

Feb 9th, 2021–Feb 10th, 2021

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

Regions

Northwest Coastal.

Outflow winds are expected to pick up and impact loose snow. Be wary of wind loaded slopes, especially where a slab builds over weak surface hoar.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

TUESDAY NIGHT - Cold and mostly clear / moderate northwest wind / alpine low temperature near -28

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

THURSDAY - Sunny / moderate to strong east wind / alpine high temperature near -18

FRIDAY - Sun with increasing cloud / moderate to strong northwest wind / alpine high temperature near -15

Avalanche Summary

On Monday, skiers were able trigger unsupported pillows failing on surface hoar down 25-40 cm near Terrace. In the north of the region, skiers found reactive wind slabs in immediate lee features in the alpine. A handful of small (size 1-1.5) natural wind slab avalanches were observed by road patrols.

On Sunday, 2 size 1 natural avalanches were reported in near Bear Pass, its likely that winds had more impact in the northern areas of the forecast region.

On Saturday, a size 2 persistent slab avalanche was intentionally triggered on a north aspect at 1200 m, failing down 35 cm on surface hoar. 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. 

Snowpack Summary

Cold temperatures are encouraging surface faceting and variable winds are impacting loose snow. Increasing outflow winds will reverse load features. 

The late January interface is down 30-70 cm, this consists of surface hoar in sheltered locations, a crust on solar features, and facets and stiff wind affected snow at upper elevations. 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.