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Archived

Avalanche Forecast

Jan 7th, 2017–Jan 8th, 2017
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Northwest Inland.

Smaller wind slabs may step-down to deeper weak layers resulting in large, destructive avalanches.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SUNDAY: Mix of sun and cloud, light easterly winds, and treeline temperatures around -20. MONDAY: Mix of sun and cloud, strong to extreme easterly ridgetop winds, and treeline temperatures around -23. TUESDAY: Mostly sunny, light to moderate easterly winds, and treeline temperatures around -15.

Avalanche Summary

Over the past week there have been a couple natural deep persistent avalanches to size 3.5. These are large, destructive avalanches that failed on sugary facets at the bottom of the snowpack and ran long distances.

Snowpack Summary

10-20 cm of recent snow with northerly winds have likely created fresh wind slabs sitting on top buried surface hoar and/or facets. Snow depth at treeline varies from about 1 m in most areas to 2 m at deeper snowpack areas in the south and west of the region, and up to 250 cm in the alpine. The shallow snowpack areas mostly consist of weak facetted or sugary grains beneath hard wind slabs. These wind slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak snow crystals near or at the ground. In addition to the facets, a thick layer of buried surface hoar may be found 20-30 cm below the surface. There is another persistent weakness that formed during the early December cold snap which is now about 40-60 cm deep. A crust from mid-November may be lurking close to the ground nestled in amongst the facets.

Avalanche Problems

Deep Persistent Slabs

This is a low probability, high consequence scenario and requires a conservative approach to larger terrain features. Avoid likely trigger spots such as steep and rocky areas with a shallow snowpack.
If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3

Wind Slabs

Recent snow and wind have created fresh wind slabs on a variety of aspects.
Use ridges or ribs to avoid pockets of wind loaded snow.Be cautious as you transition into wind affected terrain.Avoid areas where the snow feels stiff or slabby.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2