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Avalanche Forecast

Archived

Jan 27th, 2020–Jan 28th, 2020

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

Regions

South Rockies.

Lingering pockets of wind-drifted snow at higher elevation remain a concern for Tuesday. Seek out sheltered slopes and watch for reactive wind slabs around steep rolls and ridge features.

Confidence

Moderate - Confidence is due to a stable weather pattern with little change expected. Uncertainty is due to the limited number of field observations.

Weather Forecast

Monday night: Cloudy, isolated flurries, light to moderate southwest winds, alpine temperature -7 C.

Tuesday: Mix of sun and cloud, isolated flurries, light southwest winds, alpine high temperature -4 C, freezing level around 1400 m.

Wednesday: Mix of sun and cloud, moderate southwest winds, alpine high temperature -3 C, freezing level around 1400 m.

Thursday: Mostly clear, light southwest winds, alpine high temperature -1 C, freezing level around 1500 m.

Avalanche Summary

Several recent natural, large (size 2-2.5) wind slab avalanches were reported on over the past 48 hours on northwest through northeast aspects.

On January 16th, a natural, size 2 wind slab stepped down to the deep persistent basal facets below a rock band, details here.

Snowpack Summary

Recent strong west and southwest winds have formed stiff wind slabs on lee and cross-loaded terrain features at upper elevations. 

A crust can be found up to treeline and on solar aspects in the alpine due to previous warming and sun exposure. 

A well consolidated mid-pack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. Although inherently weak, the benign weather pattern this week will likely promote a decreasing trend in reactivity for this avalanche problem. Areas that are most likely to harbor this problem are shallow, rocky start zones. 

Terrain and Travel

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.