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Archived

Avalanche Forecast

Mar 19th, 2013–Mar 20th, 2013
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
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

Regions: Purcells.

Variable snowfall amounts are expected on Wednesday. Correspondingly, there may be quite a lot of local variation in avalanche danger.

Confidence

Fair - Forecast snowfall amounts are uncertain for the entire period

Weather Forecast

Wednesday: Moderate to heavy snow (15-25 cm, mostly in the west). Strong SW winds. Alpine temperature near -4.Thursday: Light snow. Moderate W winds. Alpine temperature near -14.Friday: Light snow. Light winds. Alpine temperature near -12.

Avalanche Summary

On Monday, skiers triggered several small soft slabs and sluffs on wind-loaded or steep terrain. Explosives testing triggered three large (size 2-3) slabs within the storm snow. On Sunday, a natural cycle to size 2.5 was observed in the Bugaboos on a variety of aspects in the alpine.

Snowpack Summary

Forecast storm snow is expected to create new slabs. Recent storm snow was shifted into reactive slabs by strong SW-NE winds on Monday. In some areas, the new snow was sluffing fast and far. Deep storm slabs which formed last week are slowly gaining strength. Cornices are large. A weak layer of surface hoar and/or a crust sits about 50-120 cm below the surface. It’s of most concern at alpine and treeline elevations and exhibits variable results in snowpack tests. At low elevations, a supportive crust above this layer means it's difficult to trigger. This layer may linger with ‘low probability/ high consequence’ type character. Testing for this interface in your local area should help you gain (or lose) confidence before committing to aggressive terrain. A facet/crust layer sits at the base of the snowpack in some places.

Avalanche Problems

Storm Slabs

New storm slabs are likely to develop during Wednesday’s storm. Lee loaded slopes may be particularly touchy.
Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Be cautious of sluffing in steep terrain.>Avoid steep slopes below cornices.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 6

Persistent Slabs

Storm snow, wind loading or cornice fall may overload a persistent weakness buried in the upper snowpack. This could lead to surprisingly large avalanches.
Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 7