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Avalanche Forecast

Archived

Dec 31st, 2019–Jan 1st, 2020

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

Northwest Coastal.

Avoid avalanche terrain. Heavy snowfall and strong wind have resulted in dangerous avalanche conditions.

Confidence

Moderate - A small change in the upper snowpack could dramatically change avalanche conditions.

Weather Forecast

Tuesday night: 5-15 cm of snow with rain possible below 1000 m, light wind from the south, freezing level around 1200 m with alpine high temperatures around +1 C.

Wednesday: 15-20 cm of snow, strong wind from the west, freezing level drops to 500 m and alpine high temperatures drop to -5 C.

Thursday: Scattered flurries, light variable wind, alpine high temperatures around -8 C.

Friday: 5-10 cm of snow, moderate wind from the southeast, alpine high -8 C.

Avalanche Summary

Large natural avalanches up to size 3.5 have been reported in Bear Pass since the start of the storm. The natural storm slab avalanche cycle is likely still underway with ongoing new snow and wind at higher elevations. Below treeline, loose wet avalanches will be the main concern. 

Snowpack Summary

As of midday Tuesday, 45 mm of precipitation has fallen in 48 hours. This will have fallen as snow, up to 70 cm at high elevations in the north of the region, while rain soaked the snowpack below treeline. This has resulted in a mix of surface conditions with storm slabs, wind slabs, and wet loose avalanches occurring at different elevations. As the freezing level falls Wednesday, the snowpack will lock up where it was previously moist.

The recent loading has also added stress on the two layers of surface hoar buried 70-150 cm deep. Reports from the Shames area suggest buried surface hoar can be found on all aspects, but is more prevalent on southeast to southwest aspects around 800-1400 m.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid the runout zones of avalanche paths. Avalanches could run full path.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.

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.