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Avalanche Forecast

Archived

Nov 28th, 2021–Nov 29th, 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 avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Lizard-Flathead.

Storm slabs are likely to remain reactive Monday due to an upside-down configuration in the upper snowpack and sustained warm temperatures. Continue to make conservative terrain choices at this time.

Confidence

Low - Uncertainties in both the snowpack structure and the weather forecast limit our confidence.

Weather Forecast

Sunday night: Flurries, 5-10 cm. Moderate southwest wind. Freezing level 2000 m. 

Monday: Flurries, up to 5 cm. Moderate southwest wind. Alpine temperature around 0 C. Freezing level 2000 m.

Tuesday: Flurries, up to 5 cm. Moderate to strong southwest wind. Alpine temperature around -2 C. Freezing level 1800 m.

Wednesday: Wet snow and rain, 10-25 mm. Moderate southwest wind. Alpine temperature high +2 C. Freezing level 2400 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

  • Good day to make conservative terrain choices.
  • Be aware of the potential for large avalanches due to the presence of a buried crust.
  • Avoid lingering or regrouping in runout zones.

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.