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Archived

Avalanche Forecast

Jan 13th, 2017–Jan 16th, 2017
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
1: Low
The avalanche danger rating below treeline will be low
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
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: Waterton Lakes.

The snow may feel stable below your skis, but what you don't feel are the deeper weak layers in bottom half of the snowpack.  It is unclear whether a very large natural avalanche on Friday was an isolated occurrence - use caution in open terrain.

Weather Forecast

Sun dominates the forecast, as warm dry air aloft floods in from the West.  Expect Chinook conditions: Strong Westerly winds and warm temps in the front ranges / Cooler with more Moderate winds near the divide. A strong temperature inversion will keep Alpine temps 5 degrees warmer than at Treeline. On Monday, Alpine temps may be above freezing. 

Snowpack Summary

Soft snow exists in sheltered areas, but has been stripped off or blown into Wind Slabs in open areas, especially in the Front Ranges.  A layer of facets in the middle of the snowpack seems to be slowly strengthening. Meanwhile, recent load from snow and wind may have awakened a weakening November Crust near the bottom of the snowpack.

Avalanche Summary

A Very Large (Size 3) Deep Persistent slab avalanche was observed in Alpine terrain on Friday, at 2250m on a North aspect.  A small Wind Slab stepped down in a thin area, to a layer near the bottom of the snowpack.  This propagated widely, upto 2 meters deep across a thicker slope. A Few other small Wind Slabs were observed in the Alpine.

Confidence

Due to the number of field observations

Avalanche Problems

Persistent Slabs

Facets in the midpack have produced sporadic test results, and loads in thin Alpine areas could trigger Deep Persistent Slabs on a Depth Hoar/Crust combo near the bottom of the snowpack. Near-zero temps may increase sensitivity of these layers.
Use conservative route selection, choose supported terrain with low consequence.Avoid shallow snowpack areas where triggering is more likely.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 3

Wind Slabs

Strong, gusty Westerly winds have caused variable distribution of hard Wind Slabs in open areas - pay attention on all aspects.  This problem also exists Below Treeline in the Front (Eastern) Ranges and near the Waterton Lakes.
Watch for shooting cracks or stiffer feeling snow. Avoid areas that appear wind loaded.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2