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Archived

Avalanche Forecast

Dec 8th, 2019–Dec 9th, 2019
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Glacier.

Weaknesses in the snowpack from late November could still produce very large avalanches.  Conservative use of terrain is the best way to manage this problem.

Weather Forecast

A brief ridge will give cool and relatively stable weather for the next few days.  This will be followed by another pulse of precipitation mid week.

Today: Sunny periods.  No precip. Treeline temps High -8 C. Light West winds.

Tonight: Clear periods. TL temps Low -10 C. Light West winds.

Monday: Sunny periods. TL temps High -9 C. Light west winds.

Snowpack Summary

40cm of recent storm snow (since Dec. 5th), overlies surface hoar up in sheltered locations, and is concealing evidence of the recent cycles of large to very large natural avalanches. The November 23rd surface hoar/crust/facet layer is buried 80-100+cm and remains reactive in stability tests. Tree wells are deep and deserve extra caution.

Avalanche Summary

Several large (up to size 2.5) natural avalanches were observed yesterday from steep terrain in the highway corridor.

Avalanche control Friday produced numerous size 3 and several size 3.5 avalanches.

Confidence

Due to the number of field observations

Avalanche Problems

Storm Slabs

40cm of recent storm snow has formed a slab. The new snow sits over Surface Hoar in some locations.

  • The new snow will require several days to settle and stabilize.
  • Dig down to find and test weak layers before committing to a line.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 2.5

Persistent Slabs

Storm slabs have the potential to step down to a buried weak layer (Nov 23 Surface Hoar/ Crust) now down 80-100+cm. It consists of surface hoar at treeline and below, and a crust on steep solar aspects into the alpine.

  • If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
  • Evaluate terrain features by digging and testing on adjacent, safe slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1.5 - 3.5