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Archived

Avalanche Forecast

Feb 9th, 2017–Feb 10th, 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.

Use extra caution as you transition into wind affected terrain

Confidence

Moderate - Due to the number of field observations

Weather Forecast

FRIDAY: Mix of sun and cloud / Moderate to strong southwest wind / Alpine temperature -9SATURDAY: Cloudy with isolated flurries / Moderate to strong southwest wind / Alpine temperature -7SUNDAY: Cloudy with isolated flurries / Moderate to strong southwest wind / Alpine temperature -4More details can be found on the Mountain Weather Forecast.

Avalanche Summary

On Friday, expect recently formed wind slabs to remain reactive to human triggering. Ongoing outflow winds may continue to add additional load to these wind slabs in places where there is still snow available to be redistributed. A basal weakness continues to drive a low probability/high consequence problem for the region. Very large avalanches remain possible, especially in shallow snowpack areas.No new avalanches were reported in the past few days. Most recent avalanche activity was reported last weekend, which included a remotely triggered size 2 avalanche and naturally triggered avalanches to size 2.5. Some of the natural avalanches involved the full depth of the snowpack.

Snowpack Summary

Widespread wind affected surfaces are being reported in exposed terrain including scoured surfaces, sastrugi, and hard wind slabs. In areas sheltered from the wind, the surface snow is reported to be faceting and surface hoar is developing. Below around 1400 m elevation, a rain crust can be found near the surface of the snowpack. Deeper in the snowpack, several buried surface hoar layers can be found between 30-70 cm deep. Recent reports suggest these layers have generally stabilized but isolated weaknesses may still exist, especially where buried surface hoar is still intact. A generally stiff mid pack sits above weak sugary snow near the ground. This basal weakness woke up during the last storm and produced numerous large avalanches which released on the ground. The layer is dormant for the time being but is expected to wake up with warming, heavy loading, or by the weight of a smaller avalanche stepping down.

Avalanche Problems

Wind Slabs

Recent strong to extreme outflow winds have formed hard wind slabs in leeward terrain features. These slabs are expected to remain reactive as the wind may continue to add additional load to these slabs.
Be aware of the potential for wide propagations due to the presence of hard windslabs.Be cautious as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 1 - 2

Deep Persistent Slabs

A weakness at the bottom of the snowpack is lingering. This layer may be triggered in shallow snowpack areas or by the weight of smaller avalanches.
Use conservative route selection, choose moderate angled and supported terrain with low consequence.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: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 4