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Avalanche Forecast

Archived

Jan 22nd, 2022–Jan 23rd, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Choose simple terrain, and avoid large features. Warm temperatures and sun are forecasted to hit a complicated snowpack. It's a good time to make conservative decisions, and our recent forecasters' blog explains why.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels. The snowpack structure is generally well understood.

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 Night: Partly cloudy. No new snow expected. Freezing levels fall to around 750 m.An above freezing layer (AFL) could keep temperatures above 0 C between 2500 m and 3000 m. This AFL is less likely any further north than Sparwood. 

Sunday: Partly cloudy. No new snow expected. Strong northwest wind. Freezing levels drop to 500 m overnight, rise back to 1250 m by the afternoon. AFL breaking down. 

Monday: Partly cloudy. Possible trace of snow expected. Moderate ridge wind from the northwest through northeast. Freezing levels drop to valley bottom overnight, rise back to 900 m by the afternoon.

Tuesday: Partly cloudy. no new snow expected. Strong ridge wind from the northwest. Freezing levels drop to valley bottom overnight, rise back to 1000 m by the afternoon.

Avalanche Summary

Sunshine, warm weather, and a complex snowpack are concerning this weekend. Smaller surfaces avalanches and cornice fall could trigger deep persistent slabs. 

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.

Snowpack Summary

Incoming warm air may ride on top of colder air in the valleys, so the snowpack may experience above zero temperatures at higher elevations, where you may not expect them. Combine this with the potential for strong solar input, and the alpine snowpack could experience some rapid change for the worse.

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.

Terrain and Travel

  • Choose simple terrain.
  • Avoid terrain traps where the consequence of any avalanche could be serious.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

Problems

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.