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Avalanche Forecast

Archived

Nov 29th, 2021–Nov 30th, 2021

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

Regions

Lizard-Flathead.

With little field data available, uncertainty around conditions is best managed through a conservative approach. Ease into terrain cautiously on Tuesday and watch for signs of instability.

Confidence

Low - Uncertainty is due to limitations in the field data.

Weather Forecast

Monday night: Flurries, up to 5 cm. Moderate southwest wind. Freezing level 1700 m.

Tuesday: Flurries, up to 5 cm. Strong southwest wind. Freezing level 1800 m.

Wednesday: Wet snow and rain, 10-30 mm. Strong southwest wind. Freezing level 2500 m.

Thursday: 5-15 mm rain turning to snow overnight then clearing. Moderate southwest wind. Freezing level dropping 2000 to 1700 m.

Avalanche Summary

Several natural storm slab avalanches were observed in the alpine on Sunday, a few notably stepping down to deeper layers (suspect the mid November crust).

A natural avalanche cycle occurred overnight Thursday-Friday, large storm slab avalanches (size 2-2.5) in alpine and upper treeline features were reported Friday morning. Through the day, explosives triggered large (size 2) storm slab avalanches.

Snowpack Summary

The upside-down upper snowpack consists of a 10-15 cm heavy, wet cap sitting over about 40 cm of lower density snow. Below lies a thick mid-November rain crust which has been the suspected bed surface of a few recent step-down avalanches. Moist snow is still found below the crust and to the ground.

Snowpack depths range from 40-70 cm at treeline elevations. Expect to find a deeper snowpack at higher elevations and in wind-loaded areas. Snowpack depths decrease rapidly below 1500 m.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Make observations and assess conditions continually as you travel.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Be aware of the potential for large avalanches due to the presence of a buried crust.

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.