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Avalanche Forecast

Archived

Dec 23rd, 2019–Dec 24th, 2019

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

Regions

South Coast Inland.

Very dangerous avalanche conditions exist in the South Coast Inland - particularly in the north of the region. This is a time for very conservative terrain selection and the avoidance of most avalanche terrain at higher elevations. 

Confidence

Moderate -

Weather Forecast

Monday night: Becoming cloudy. Isolated flurries in the south of the region. Light southwest winds.

Tuesday: Cloudy with isolated flurries in the north of the region, continuing overnight. Light southwest winds. Alpine high temperatures around -8.

Wednesday: Mainly cloudy, with cloud decreasing.Light northeast winds. Alpine high temperatures around -8, closer to -6 in the south of the region.

Thursday: A mix of sun and cloud. Light to moderate southwest winds. Alpine high temperatures around -7.

Avalanche Summary

A widespread avalanche cycle was observed across the region on Friday and Saturday. Avalanches were reported to be running to valley-bottom in the north of the region, failing on the weak layer described in the snowpack summary below.

Human-triggered avalanches are expected to be very likely to occur on Tuesday at higher elevations, particularly in the northern half of the region (e.g., Duffey, Hurley, etc.). See this MIN report of an avalanche involvement on Monday for an example of the issue at hand.

Given our current snowpack structure, we recommend avoidance of alpine avalanche terrain and very conservative decision-making at treeline.

Snowpack Summary

Over 120 cm of snow accumulated in the south of the region with the recent storm and over 40 cm in the north of the region. The snow fell with strong southwest wind. This snow is likely gaining strength as the days pass but still has the possibility of being triggered by a person or machine.

Depending on your location, the above-mentioned storm snow may be straining a now deeply buried weak layer composed of sugary faceted grains and hard melt-freeze crust from mid-November. This structure is a recipe for large and destructive avalanches and a problem that may persist for weeks to months. The layer certainly exists in the north of the region but it is uncertain to what degree it is a problem in the south of the region.

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Persistent slabs have potential to pull back to lower angle terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.

Problems

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.

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.