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Avalanche Forecast

Archived

Dec 11th, 2021–Dec 12th, 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 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast.

Ongoing snow and wind will keep avalanche hazard elevated. Avoid freshly wind-drifted areas and continue to make conservative terrain choices while the storm snow gains strength.

Confidence

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

Weather Forecast

Saturday night: Cloudy, 10-20 cm of snow above 400 m, moderate southwest wind, treeline temperatures near -6 C.

Sunday: Cloudy, 10-20 cm of snow above 500 m, moderate southwest wind, treeline temperatures near -4 C. 

Monday: Cloudy, 15-30 cm of snow above 600 m, winds becoming southeast and increasing to moderate, treeline temperatures near -3 C.

Tuesday: Mostly clear, light variable wind, treeline temperatures near -6 C, freezing level around 200 m.

Avalanche Summary

We expect natural and human triggered avalanche activity to continue on Sunday.

There are no recent reports from the region. We expect that a natural avalanche cycle occurred early on Saturday at the height of the storm.

Snowpack Summary

Intense bands of precipitation are forecast to bring another 10-30 cm of cold, light snow to the mountains in a highly localized pattern. Sustained southwest winds will have an ongoing supply of snow to drift into reactive wind slabs at upper elevations. Avoid freshly wind-loaded terrain features on Sunday (for example, down-wind of ridges and roll-overs).

A powerful storm on Friday night brought 30-70 cm of new snow to the mountains with strong southwest winds. A gradual temperature rise during the storm created warmer denser snow over colder lighter snow. In many locations, storm accumulations sit on crust layers that formed in early December. This tricky combination of slab and sliding surface may require more time to recover and gain strength, and it warrants careful evaluation and cautious routing-finding.

Below the early December crust layers, the snowpack is generally well-settled. With this storm event, a greater number of areas at treeline elevations may meet the threshold for avalanches.

Terrain and Travel

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.
  • Don't let the desire for deep powder pull you into high consequence terrain.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.