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Avalanche Forecast

Archived

Feb 11th, 2022–Feb 12th, 2022

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

Regions

South Coast Inland.

Warm and sunny conditions are keeping the danger elevated. Weak cornices and loose wet avalanches should expected during the heat of the afternoon.

The biggest concern remains a weak layer down 20-70 cm which is still capable of producing very large and destructive avalanches.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

A ridge of high pressure brings very warm and sunny conditions which are expected to persist until the end of Sunday. A temperature inversion is expected with cooler temperatures in the valleys. 

Friday night: Clear, light N wind, freezing levels around 2800 m.

Saturday: Sunny, light variable wind, freezing levels around 2800 m.

Sunday: A mix of sun and cloud, light to moderate SW wind, freezing levels dropping to around 2500 m. 

Monday: Light snow, moderate variable wind, freezing levels 800-1200 m. 

Avalanche Summary

On Thursday, some small loose wet avalanches were reported on steep sun-exposed slopes. 

Last weekend, several very large human-triggered avalanches occurred on the late-January persistent weak layer in the north of the region. This layer is now sitting dormant but there is serious concern that it is going to wake up with sun and very warm temperatures this weekend. The layer is down 20-70 cm so it is still in the prime depth for human-triggering. Cornice releases are also a major concern for triggering persistent slabs so give extra caution to overhead slopes which are exposed to cornices. Some avalanche activity also occurred on the layer in the south of the region but the avalanches were generally smaller with less propagation and the layer generally appears to be less reactive in the south.  

Snowpack Summary

A widespread surface crust is expected to have formed Thursday night. This crust may have broken down on steep sun-exposed slopes during the afternoon. Crust formation is expected to continue Friday night with clear skies in the forecast but will likely break down again on steep sun-exposed slopes on Saturday afternoon. Prior to the warming and sun, strong winds had caused extensive wind effect and wind slab formation in exposed terrain at higher elevations. 

The primary concern in the snowpack is the late-January weak layer down 20 to 70 cm. This layer is primarily composed of a crust and facets, but also may include surface hoar in more sheltered areas around treeline elevation. The interface is most prominent between 1700 and 2000 m in the north of the region and it has been found on all aspects in the Duffey Lake area. This layer is up to around 90 cm deep in the south of the region and while it did produce some avalanches last weekend, it does not seem to be as reactive as it is in the north of the region.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Remote triggering is a concern, avoid terrain where triggering slopes from below is possible
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Extra caution is needed around cornices under the current conditions.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.

Problems

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.

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.