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Avalanche Forecast

Archived

Feb 1st, 2022–Feb 2nd, 2022

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

Regions

Northwest Inland.

New snow and strong winds are driving the avalanche danger to CONSIDERABLE. Wind slabs may be touchy and easily triggered due to the old weak snow surfaces they have formed on. 

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Tuesday Night: 5-10 cm of new snow with strong northwest winds at ridgetop. Alpine temperatures near -15 and freezing levels valley bottom.

Wednesday: Another 5-10 cm of snow with continued strong winds switching from the northwest to the west- southwest. Alpine temperatures near -10. Freezing levels valley bottom.

Thursday/ Friday: Mix of sun, clouds, and flurries near 10 cm with strong southwest wind at ridgetop. Average alpine temperature near -5 and freezing levels 1000 to 1600 m. 

Avalanche Summary

A natural wind slab avalanche cycle occurred on Monday up to size one. No new reports by Tuesday afternoon. 

New snow and strong wind from the NW then SW will likely build fresh and reactive wind slabs on Wednesday.

Snowpack Summary

Another 10-15 cm of new snow is forecast by Wednesday afternoon. This will add to the recent 15 cm that has fallen over a variety of surfaces including facets, surface hoar, and old wind slab. The new snow will likely not bond well to these surfaces. In the southern part of the region, it is possible to find a rain crust up to 1500 m.

Below this we have two persistent weak layers, the first is a surface hoar layer from mid-January buried down 20 to 30cm. The second is a layer of facets from early January which is now down 50 to 80cm, it has been most reactive where wind slab has formed above it and will now likely require a large load to trigger.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

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.