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Avalanche Forecast

Archived

Nov 30th, 2021–Dec 1st, 2021

Alpine
Widespread avalanches certain.
Treeline
Widespread avalanches certain.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

North Columbia.

A widespread large natural avalanche cycle will take place starting late Tuesday night and will continue through Wednesday. Avoid all avalanche terrain.

Confidence

High - We are confident a natural avalanche cycle will begin shortly after the arrival of the incoming weather.

Weather Forecast

Tuesday night: As the storm builds throughout the day freezing levels will once again rise to 2000m with strong southwest winds in the Alpine. 15 to 30mm of precipitation is expected.

Wednesday: the storm will reach its peak early in the morning. Freezing levels will rise to 2300 and fall slightly throughout the day. Another 30mm of precipitation is expected with strong Southwest winds.

Thursday: Freezing levels will fall to 1400m with some lingering flurries in the wake of the storm. winds will be moderate from the West.

Friday: A ridge of high pressure will mean clear skies and light alpine winds. Freezing level will be at or near valley bottom.

Avalanche Summary

Storm slabs will build throughout the night and following day. Natural avalanche activity is certain with this next weather system. Avalanches will run full path to lower elevations like the valley or simple, below treeline terrain. 

On Monday, reports indicated several natural wet loose avalanches from 900-1200 m (below treeline) up to size 2.

Snowpack Summary

The next storm will bring as much as 60mm of precipitation. Most of which will fall as rain due to the high freezing level meaning a saturated snowpack at lower elevations. At higher elevations the new snow will add to the already large storm and wind slab problem.

 

The average snowpack depth at treeline is 250 cm. The mid-November rain crust can be found down 70 to 130 cm and exists around 1900 m and below. 

Terrain and Travel

  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.

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.