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Avalanche Forecast

Archived

Nov 29th, 2021–Nov 30th, 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 and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast.

New snow followed by heavy rain is Tuesday's recipe for rapidly changing and dangerous avalanche conditions.

Confidence

High -

Weather Forecast

Monday night: Cloudy with increasing wet flurries bringing 5-10 cm of new snow. Moderate southwest winds. 

Tuesday: Wet flurries transitioning to heavy rain in the afternoon; 30-50 mm accumulation. Strong south or southwest winds, increasing over the day and overnight. Treeline temperatures rising from around 0 to +4 over the day as freezing levels climb from 1400 to 2900 metres.

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

Thursday: Mainly clear. Light to moderate northwest winds. Treeline high temperatures around -4.

Avalanche Summary

Tuesday's forecast suggests we will see a rapid evolution of avalanche conditions over the day. Depending on freezing levels and snowline elevations, we could see substantial storm slabs form in the region's upper elevations before they are hammered by rain in the afternoon. A rapid transition from widespread touchy storm slabs to equally touchy wet loose avalanche conditions is expected to occur over the day. 

Snowpack Summary

Heavy rain has affected the snowpack at all elevations. The current forecast suggests we may see 15-25 cm of new snow accumulate before Tuesday afternoon when heavy rain takes over and once again drenches the snowpack at all elevations.

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

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • The first few hours of rain will likely be the most dangerous period.
  • The more the snow feels like a slurpy, the more likely loose wet avalanches will become.

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.