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Avalanche Forecast

Archived

Dec 22nd, 2019–Dec 23rd, 2019

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

Regions

South Coast Inland.

Clear skies may lure you into bigger terrain, but this is not the time to expose yourself. The recent snow may remain touchy and it is resting on a weak layer in parts of the region. Read more here. Best to avoid alpine avalanche terrain and travel conservatively at treeline.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SUNDAY NIGHT: Clear skies in the north of the region and cloudy with light snowfall in the south of the region, accumulation 2 to 5 cm, light northwest wind, alpine temperature -6 C, freezing level below valley bottom.

MONDAY: Mostly clear skies, light southwest wind, alpine temperature -7 C, freezing level below valley bottom.

TUESDAY: Mostly cloudy with isolated flurries, accumulation 1 to 3 cm, light southwest wind, alpine temperature -9 C, freezing level below valley bottom.

WEDNESDAY: Mostly cloudy with isolated flurries, accumulation 1 to 3 cm, light northwest wind, alpine temperature -8 C, freezing level below valley bottom.

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.

Human-triggered avalanches are expected to be very likely to occur on Monday at higher elevations, particularly in the northern half of the region (e.g., Duffey, Hurley, etc.). We recommend avoidance of alpine avalanche terrain and very conservative decision-making at treeline, given this weak snowpack.

Snowpack Summary

Over 120 cm of snow has 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 has the possibility of being triggered by human traffic.

The snow may be loading a weak layer of sugary faceted grains and hard melt-freeze crust buried mid-November, which 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 unclear whether 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.