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Avalanche Forecast

Archived

Feb 20th, 2022–Feb 21st, 2022

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

North Columbia.

Continually assess the bond between new snow and the old surface. Be extra cautious in wind-loaded terrain.

Do not underestimate the influence of the sun on a cold, clear day. Avalanche danger could increase rapidly on sun-exposed slopes when solar radiation is strong.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Bundle up in your warmest gear, arctic air is here! 

Sunday Overnight: Cloudy with light flurries, clearing into the morning. Light to moderate northerly winds. Alpine temperatures plummet to around -20 C.

Monday: Mainly clear and cold. Light northerly winds. Alpine temperatures around -25 C.

Tuesday: Cold and clear. Light northerly winds. Alpine temperatures around -20 C.

Wednesday: Cloudy with light flurries. Light to moderate northwesterly winds. Alpine temperatures around -16 C.

Avalanche Summary

During the peak of the storm on Saturday, numerous natural and human-triggered storm slabs were reported on all aspects due to rapid loading. Larger natural and human-triggered wind slab avalanches were reported in wind-loaded terrain in the alpine and treeline. Several natural dry loose avalanches were reported out of steep terrain on all aspects. 

Explosive control last week initiated some larger persistent slabs up to size 3. 

Snowpack Summary

This weekend's storm brought 20-70 cm of new snow above 1400 m. At lower elevations, a surface crust can be expected from wet snow/rain throughout the storm. Up to 120 cm now overlies the old, hard surface, which is a result of a period of high pressure in mid-February. The layer is comprised of facetted snow, a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. 

The mid-January surface hoar/crust layer is now down 50-150 cm in the snowpack. This layer has not been reactive to skier traffic in the past week and is showing limited reactivity in snowpack tests. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche stepping down to this layer. 

The facet/crust layer that formed in early December is now buried around 150 to 250 cm. Human triggering of this layer is unlikely, except perhaps on a re-loaded bed surface or in a shallow snowpack area. This layer may become a concern during periods of warming or heavy loading. 

Terrain and Travel

  • Closely monitor how the new snow is bonding to the old surface.
  • Use small low consequence slopes to test the bond of the new snow.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.