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Avalanche Forecast

Archived

Jan 19th, 2022–Jan 20th, 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, 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.

Regions

South Rockies.

Wind slabs may exist below ridgecrest on leeward slopes and loose-dry sloughing may be easily triggered from steeper terrain features.

Be mindful of the lingering deep persistent slab problem. Caution on shallow snowpack areas and thin to thick steep rocky zones.

Confidence

Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

Thursday Night: Increasing cloud cover later in the evening with isolated flurries. Ridgetop wind light from the southwest and alpine temperatures near -10. 

Thursday: Mix of sun and cloud. Moderate ridgetop wind from the southwest. Alpine temperatures warming to near -5 and freezing levels valley bottom.

  

Friday: Mix of sun and cloud. Ridgetop wind light from the West. Alpine temperatures near -5 and freezing levels valley bottom.

Saturday: Potential for inversion with valley cloud and cooler temperatures down low and sunshine in the alpine. Alpine temperatures near -3 and below freezing in the valleys.

Avalanche Summary

No new reports by Wednesday afternoon.

Recent deep persistent slab avalanches were reported in neighboring regions (Lizard-Flathead and Waterton National Park) over the last few days. These human-triggered and natural avalanches failed on the early December crust and showed wide propagation. This evidence suggests the deep persistent slab problem is still a concern in the region. 

Snowpack Summary

The region received up to 25 cm by Tuesday, which now overlies older surfaces like hard wind slabs or a recent melt-freeze crust. The crust varies from thin/breakable to thick/supportive, according to the aspects and elevation. Under it, the snowpack consists of a variety of old surfaces, including soft snow in sheltered areas and wind slabs in exposed and open areas. 

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now typically down 80-150 cm. In the neighboring Lizard-Flathead region, three very large avalanches were reported on this layer on January 13. This layer has created a tricky low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch your sluff: it may run faster and further than you expect.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Conditions may have improved, but be mindful that deep instabilities are still present.

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.