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Avalanche Forecast

Archived

Feb 1st, 2021–Feb 2nd, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

Wind slabs at upper elevations continue to be touchy to skier and rider triggers, especially where they sit above a buried surface hoar/ crust layer.

Confidence

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

Weather Forecast

Tuesday: A mix of sun and cloud with isolated flurries. Ridgetop wind light from the northeast. Alpine temperatures near -6 and freezing levels valley bottom. 

Wednesday: Snow 5 cm with light ridgetop wind. Alpine temperatures near -6 and freezing levels in the valley bottom.

Thursday: Snow up to 20 cm. Ridgetop wind strong from the southwest and freezing levels rising to 1300 m. 

Avalanche Summary

Several small wind slab avalanches were triggered by skiers and riders at treeline and in the alpine on various aspects on Saturday and Sunday (see this MIN report). 

As the slab properties start to change, and the recent snow becomes more cohesive (under the influence of wind and settlement) it will likely remain reactive to human triggers, especially where it sits above a surface hoar interface. 

Snowpack Summary

15-45 cm of recent snow sits on a crust below 1000 m and surface hoar in sheltered locations at and below treeline. If the recent snow has enough cohesion the slab may be reactive where it sits above these weak layers. This MIN report shows just that.

The layers in the mid and base of the snowpack have gained strength with high snowfall amounts in January. Deeper layers appear to have gone inactive in the southern part of the region. However, in the northern part of the region (e.g. Bear Pass, Ningunsaw) there has still been regular avalanche activity on weak snow at the bottom of the snowpack with large loads such as explosives or cornice collapses.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch your sluff: it may run faster and further than you expect.

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.