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Avalanche Forecast

Archived

Dec 11th, 2021–Dec 12th, 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 possible, human triggered probable.
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, human triggered possible.

Regions

Northwest Coastal.

Southwest wind has combined with 40 to 100 cm of snow over the last few days, although the storm is tapering off, natural avalanches remain possible. Avoid wind exposed terrain and terrain traps Sunday as the storm snow continues to settle and stabilize.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

We’re slowly moving into a period of high pressure.

SATURDAY NIGHT: A few cm of snow overnight with moderate southwest wind, freezing level at valley bottom.

SUNDAY: Broken cloud cover, freezing level at valley bottom, light to moderate wind generally out of the south, 1 to 5 cm of snow possible.

MONDAY: Scattered cloud cover, freezing level at valley bottom, moderate to strong east/southeast wind, no significant precipitation expected.

TUESDAY: Clear skies at dawn with cloud cover increasing after lunch, freezing level at valley bottom, light southwest wind, no significant precipitation expected.

Avalanche Summary

Recent observations are limited, but there was quite a bit of avalanche activity in the storm snow on Friday, with soft slabs and dry loose avalanches running naturally to size 2. 

If you do head into the backcountry, please share you observations to the Mountain Information Network!

Snowpack Summary

Between Friday at noon and Saturday late afternoon there has been 20 to 35 cm of new snow across the southern half of the region, and 15 to 20 in the North around Bear Pass. This brings total storm accumulations across the region to betweeh 40 and 100+ cm over the last few days. Strong southwest wind has no doubt formed fresh + potentially sensitive slabs in wind exposed terrain.

There is still some concern for buried weak layers, will the possibility for buried surface hoar and faceting above the December 1st crust, now buried 40-120 cm deep. In the southern part of the region the December 1st crust has been reported up to 2000 m, tapering to 500 m in the northern reaches. The Terrace area has reported the crust to around 1200 m.

Snowpack depths range from 150 cm- 300 cm at treeline and 200 cm- 400 cm in the alpine.

Terrain and Travel

  • Give the new snow time to settle and stabilize before pushing into bigger terrain.
  • Be aware of the potential for large, avalanches due to the presence of buried crust/facet combo.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.