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Avalanche Forecast

Mar 5th, 2014–Mar 6th, 2014
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
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
3: Considerable
The avalanche danger rating below treeline will be considerable
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
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: Northwest Inland.

Snow is finally on the horizon! We're expecting a rapid change from cold and dry to moist and mild on Friday. This sudden change could be enough to wake up the mid February weak layer and produce large avalanches.

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Thursday: Cloudy with sunny breaks and a chance of flurries. The freezing level is at the surface. Ridge winds are light to moderate from the S-SW. Friday: Moderate snowfall – 10-20 cm. The freezing level climbs to 800 m in the south and remains near valley bottom in the north. Winds are strong from the S-SW. Saturday: Light to moderate precipitation. The freezing level is between 1000 and 1500 m. Winds are moderate to strong from the SW.

Avalanche Summary

No new avalanche activity reported. Expect this to change on Friday with forecast snowfall, warming and strong winds.

Snowpack Summary

Persistent cold dry weather has resulted in significant new surface hoar growth and surface facetting on shady slopes at all elevations. Steep solar aspects may have a sun crust. The early February weak layer of facets, crusts, and surface hoar is buried down about 35-80 cm. The snow above the crust has been transported by Southwest winds and then reverse loaded by Easterly or Southeast winds. Cold temperatures have not settled the snow above the weak layer into a cohesive slab, and the cold has preserved the weak layer and associated crusts. I suspect that there will not be much change or improvement in the bonding of the late February snow to the crusts and facets. Snow pack tests may help to show when this layer demonstrates more resistance to added forces.

Avalanche Problems

Persistent Slabs

Cold temperatures have likely helped to preserve the mid February persistent weak layer, down 30-80 cm. This layer could become active on Friday with new loading from snow and wind, and rapidly rising temperatures. 
Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 5

Wind Slabs

Continued easterly outflow winds are expected to scour leeward slopes and develop hard wind slabs in areas that have snow available for transport.
Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 3