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

Regions

Vancouver Island.

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

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels.

Weather Forecast

Monday night: Cloudy with flurries bringing 10-15 cm of new snow. Strong southwest winds.

Tuesday: Moderate snowfall switching to heavy rain by about noon; 15-35mm over the day and increasing overnight. Strong to extreme southwest winds. Treeline temperatures rising from 0 to +5 as freezing levels climb from 1400 to 3000 metres.

Wednesday: Continuing heavy rain switching to light snowfall late in the afternoon. Minimal accumulation. 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: Clearing. Light west winds. treeline high temperatures around -5.

Avalanche Summary

Looking forward to Tuesday, new snow accumulations from overnight and the early part of the day will be impacted by heavy rain. This should set up a rapidly changing risk scenario where a building storm slab problem transitions to active wet loose avalanche conditions over the day.

Snowpack Summary

Heavy rain has affected the snowpack at all elevations. Surface crusts have likely formed at all but the lowest elevations holding snow cover. Forecast weather should add brief new snow accumulations before heavy rain drenches the snowpack once again. 

Early indications of our region's existing (but eroding) snowpack suggest alpine snowpack depths around 150 cm, 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

  • 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.