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Avalanche Forecast

Archived

Nov 30th, 2021–Dec 1st, 2021

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

Regions

Vancouver Island.

Heavy rain followed by alpine snowfall is Wednesday's recipe for rapidly changing and dangerous avalanche conditions.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels.

Weather Forecast

Tuesday night: Rain; 20-40mm. Extreme southwest winds.

Wednesday: Continuing rain switching to light snowfall late in the afternoon. 10-15 cm accumulation, mainly in alpine. Strong southwest winds easing over the day. Treeline temperatures dropping from about +4 to 0C over the day as freezing levels return to about 1500 metres.

Thursday: Mainly sunny. Light to moderate northwest winds. Treeline high temperatures around -5.

Friday: Mainly sunny, clouding over in the afternoon. Light variable winds. Treeline high temperatures around -3.

Avalanche Summary

Looking forward to Wednesday, heavy rain will continue to promote wet loose avalanche activity earlier in the day. Tapering precipitation and falling freezing levels will be tightly linked as the storm ends, meaning there is a chance for dry snow to accumulate at higher elevations before the end of the day. There is concern for touchy new wind slabs forming in leeward terrain at higher elevations during this period.

Snowpack Summary

Heavy rain has affected the snowpack at all elevations. Light new snow amounts may accumulate at high elevations during the final hours of the storm on Wednesday. Strong surface crusts should form at all elevations over Wednesday night and effectively lock the snowpack in place underneath any new accumulations.

Recent indications of our region's existing (but eroding) snowpack suggested alpine snowpack depths around 150 cm, with depth tapering dramatically with elevation to about 30-60 cm at treeline. Snow cover is thin and generally below threshold for avalanches below about 1300 metres. 

Terrain and Travel

  • As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
  • Keep in mind that wet avalanches can be destructive due to their high density.
  • Wind slabs are most reactive during their formation.
  • Be alert to conditions that change with elevation.

Problems

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.