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Avalanche Forecast

Archived

Nov 30th, 2021–Dec 1st, 2021

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

Regions

South Coast.

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: Heavy rain; 30-40mm. Strong to extreme south or southwest winds.

Wednesday: Heavy rain; 40 mm accumulation. Strong south or southwest winds. Treeline high temperatures around +4.

Thursday: Mainly sunny. Light variable winds. Treeline temperatures of -1 to -4, dropping over the day.

Friday: Mainly sunny, clouding over in the afternoon. Light variable winds. Treeline high temperatures around -1.

Avalanche Summary

Wednesday's forecast suggests we may see another day of rapidly evolving avalanche conditions. If daytime freezing levels fall low enough we could see substantial storm slabs form in the region's upper elevations before the end of the day, particularly in alpine areas. A rapid transition from active wet loose avalanche conditions to a touchier new storm slab problem should be on your mind as new snow begins to accumulate.

Snowpack Summary

Heavy rain has affected the snowpack at all elevations. Significant new snow (15-30 cm) may accumulate at high elevations during the final hours of the storm on Wednesday. This could set up a scenario where unstable new storm slabs become a serious concern before the end of the day.

Average treeline snow depths are around 80-100 cm with much of treeline and all but the uppermost below treeline elevations still below threshold depths for avalanches.

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.
  • Dial back your terrain choices if you are seeing more than 20 cm of new snow.

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.

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.