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Avalanche Forecast

Archived

Feb 20th, 2022–Feb 21st, 2022

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

Regions

Northwest Inland.

Shifting winds have formed wind slabs on a variety of aspects. At this time of year the sun can have a surprisingly powerful effect on the snow. Strong solar radiation can weaken cornices and initiate point releases in powdery snow especially on steep rocky south facing slopes.

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

Sunday night: Clearing, light northwest wind, low of -20.

Monday: Sunny, moderate northeast wind, high of -14.

Tuesday: Increasing cloud in the afternoon, light to moderate northeast wind switching northwest, high of -12.

Wednesday: A mix of sun and cloud, moderate northwest, high of -8.

Avalanche Summary

A natural size 2 wind slab was observed on a northeast aspect in the alpine during the strong wind event on Saturday. Previous natural activity observed on Thursday was limited to size 1-1.5. 

Several skier triggered wind slabs size 1-1.5 have been reported over the past few days, most in predictably wind loaded lees or convexities, near ridgetop, around treeline or higher.

Snowpack Summary

10-20 cm of recent snow has been extensively wind affected at upper elevations, with exposed windward features scoured down to the crust. Below 1300 m, a surface crust has formed over moist snow.

The recent snow sits over a 10-20 cm thick rain crust which effectively caps the underlying snowpack, making human triggering of avalanches on weak layers deeper in the snowpack very unlikely. Large cornice failures may still have potential to trigger these deeper layers.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.