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Avalanche Forecast

Archived

Jan 20th, 2022–Jan 21st, 2022

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

Regions

South Rockies.

Strong wind and recent snow may have formed pockets of reactive wind slab.

Be mindful of the lingering deep persistent slab problem. Forecast warming temperatures and sunshine this weekend may wake this problem up and trigger very large and destructive avalanches.

Confidence

Low - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

A lot of uncertainty exists with the timing and persistence of the warming that is forecast for Saturday onward.

Friday: Mix of sun and cloud with no new snow and strong westerly ridgetop winds. Alpine temperatures near -5 and freezing levels at the valley bottom.

Saturday: The region may start to see some warming with the potential for an upper inversion (warmer air aloft 1500-2000m) bringing valley clouds and some sunny skies in the alpine. Alpine temperatures near 0 to -2 degrees. Below freezing in the valley bottoms.

Sunday: Mix of sun and cloud with isolated flurries. Alpine temperatures near 0 to -1. Ridgetop winds light from the West and freezing levels 1900 m.

Avalanche Summary

No new reports on Thursday.

Recent deep persistent slab avalanches were reported in neighboring regions (Lizard-Flathead and Waterton National Park) over the past week. 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, especially through the weekend with warming.

Snowpack Summary

Strong winds have redistributed the recent storm snow onto leeward slopes forming pockets of isolated, stiff wind slabs. The wind slabs may be more reactive where they sit above older hard snow surfaces or crusts that extend to 2100 m. The crust varies from thin (unsupportive below 1800 m) to thick (supportive above 1800 m). Below this is a well-settled mid-pack down to the early December crust/facet interface.

The crust that was formed in early December 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. However, with warm temperatures forecast this weekend we could see this layer wake up and produce very large and destructive avalanches. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs may be poorly bonded to the underlying crust.
  • 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.