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Archived

Avalanche Forecast

Mar 16th, 2013–Mar 17th, 2013
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
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
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Northwest Coastal.

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Synopsis: Northwest flow with limited moisture will bring cooler temps and flurries through the period.Sunday and Monday: Flurries, with some breaks in the cloud giving daytime warming both days. Afternoon freezing level around 500 m. Winds light westerly, becoming northwesterly on Monday.Tuesday: Light snowfall starting late in the day. Freezing level 200 m. Winds light southerly.

Avalanche Summary

On Saturday, natural slab avalanches were reported up to size 2.5 on north to east aspects in the alpine. Many were suspected of being triggered from cornice releases. Also on Saturday, loose snow avalanches were reported from steep terrain on solar aspects. On Friday, a skier triggered a size 2 avalanche on the March 9th surface hoar layer with a crown depth of 45 cm. Several other skier-triggered avalanches occurred on north and west aspects on the same weak layer.

Snowpack Summary

25-50 cm of recent storm snow rests on a variety of old snow surfaces, including crusts, previous wind slabs and surface hoar. Warmer temperatures and recent winds have now set this new snow into a reactive slab, with wind slabs building in exposed lee areas. The surface hoar (buried March 9th) is reported to be well-developed and fairly widespread, at treeline and alpine elevations. Recent snowpack tests have produced sudden failures with moderate loading force at this interface. The mid snowpack is generally well settled and strong. Cornices are large and untrustworthy, especially when the sun is out.

Avalanche Problems

Storm Slabs

Recent new snow has consolidated into a slab and is reacting on steep terrain, particularly on north and east aspects in the alpine. The underlying weak layer of surface hoar is quite touchy.
Choose conservative lines and watch for clues of instability.>Avoid freshly wind loaded features.>Avoid open slopes and convex rolls where buried surface hoar may be preserved.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 5

Cornices

Do not travel on slopes that are exposed to cornices overhead.>Stay well to the windward side of corniced ridges.>

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

Elevations: Alpine.

Likelihood: Likely

Expected Size: 2 - 6