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Avalanche Forecast

Archived

Jan 21st, 2022–Jan 22nd, 2022

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.
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 have formed reactive wind slabs.

Warm temperatures combined with a lingering deep persistent slab problem may equal large and destructive avalanches. Its a good time to approach the mountains cautiously and even expect surprises.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A ridge of high pressure brings warming and sunny skies through the weekend. Valley bottoms may see some valley cloud trapping cooler air down low.

Saturday: Freezing levels rise through the day to 2000-2500 m with generally clear skies. Possible inversion especially in tighter valleys may hold valley cloud and cooler temperatures down low. Ridgetop winds moderate from the northwest. Expect some cooling overnight.

Sunday: Sunshine and freezing levels hovering around 2000-2500 m. Strong northwest wind. 

Monday: Freezing levels forecast to drop to 1000 m.

Avalanche Summary

On Friday morning the field team reported four new wind slabs size 2.5 to size 3 that looked to fail on the (re-loaded) early December interface in the Crowsnest North. One of these appeared to be triggered by a cornice fall.

Sunshine, warm weather, and a complex snowpack are concerning this weekend. Smaller surfaces avalanches and cornice fall could trigger deep persistent slabs. This layer has been dormant but to no surprise could wake up. 

Snowpack Summary

Strong winds have redistributed the recent storm snow from earlier this week onto leeward slopes forming stiff and reactive wind slabs. The wind slabs prove to be more reactive where they sit above older hard snow surfaces or a crust. 

The upper snowpack is variable throughout the region with a melt-freeze crust found 10-20 cm down (aspect and elevation dependant) in some locations to barely existing in other locations, especially above 2000 m. One common theme throughout the region is that the mid-pack is well settled above the deeper December crust/facet interface which is currently the primary concern in the snowpack.

The early December crust is now generally down 80-150 cm. This layer is found widespread through the region but with varying test results. Recent snowpack tests have shown more reactivity in shallower snowpack areas as well as reactivity to step down avalanches. This indicates that there is potential to trigger this weak layer from a thin spot which may propagate to a thicker slab within the snowpack. In turn, triggering a very large avalanche. 

Most concerning is the warm weather this weekend and its effect on the complex snowpack. Warming, solar radiation, and cornice fall could all play a role in triggering deep persistent slabs. This layer has been dormant but to no surprise could wake up. 

Terrain and Travel

  • Cornices become weak with daytime heating.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.

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.