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Avalanche Forecast

Archived

Nov 30th, 2021–Dec 1st, 2021

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

Regions

South Coast Inland.

AVOID ALL AVALANCHE TERRAIN. A natural avalanche cycle is expected overnight Tuesday with very large avalanches running full path. Very dangerous conditions will persist through Wednesday.

Confidence

High -

Weather Forecast

Tuesday night: Periods of snow and rain, Rain as high as 2300 metres. Strong to extreme southwest winds. Freezing level peaking at 2500 metres.

Wednesday: Continuing snowfall bringing 10-30 cm of new snow. Rain below about 1600 metres. Strong to extreme southwest winds. Treeline high temperatures around 0C with freezing levels between 1800-2000 metres.

Thursday: Mainly sunny. Light southwest winds. Treeline high temperatures around -7 with freezing levels back to 800 metres.

Friday: Initially clear but clouding over by afternoon. Light variable winds. Treeline high temperatures around -7.

Avalanche Summary

Large avalanches sliding on recently buried surface hoar and deeper buried crusts have been observed in the region as well as in the neighbouring Sea to Sky. With another atmospheric river storm continuing to pummel the region through Wednesday, we expect to see a widespread avalanche cycle with the potential for large, full-path avalanches.

Snowpack Summary

Heavy snowfall and strong southerly winds continue to develop storm slabs in the alpine and at treeline, with thicker accumulations in leeward features. All this new snow sits over a layer of surface hoar down 70-100 cm and a deeper crust/facet combo layer that produced large avalanches during Saturday's storm. Heavy loading and warming coming with this intense storm will likely produce more avalanche activity on these layers.

Average snowpack depths in the alpine are now 130-180 cm. Below treeline, depths of 30-50 cm have been reported around 500 m, decreasing dramatically with elevation, and still below threshold for avalanching in many areas. Early season hazards such as rocks, stumps, and creeks are a concern below the alpine.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • Be aware of the potential for large, deep avalanches to run full path or even longer.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.