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Archived

Avalanche Forecast

Jan 14th, 2013–Jan 15th, 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
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
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

Regions: Kootenay Boundary.

I’ve based this forecast on a weather model that shows rapidly increasing alpine temperatures on Tuesday. If it doesn’t warm up, then these danger ratings are one notch too high.  See the forecasters blog for warming details.

Confidence

Poor - Freezing levels are uncertain for the entire period

Weather Forecast

Tuesday: Winds out of the NW at extreme values. Freezing level rising to 2300m+ around lunch time.  No snow/rain. Clearing skies.Wednesday: Freezing level stays high around 2300m.  Strong NW winds persist.  No precip expected.Thursday: Freezing level comes down to 2000m.  Winds switch to westerly strong.  Increasing to westerly extreme in the afternoon.

Avalanche Summary

Skiers are still triggering some sluffing in steep terrain.  A small slab popped out Saturday night and there was also a report of a skier controlled size 1 failing on facets 20 cm below the snow surface. Avalanche activity is fairly benign at the moment.

Snowpack Summary

Winds picked up out of the west Sunday creating a thin wind slab 5 - 15cm thick in open alpine and treeline features.Under this new wind slab 65 cm of settled snow rests on the January 4th interface which consists of small facets, surface hoar (up to 12mm) in sheltered treeline and below treeline areas and sun crust on steep south and west facing slopes. The bonds at this interface are improving.? The layer is still alive and well in test pits but has not been reactive to human triggering in the last day or so.? Wind slabs created by the previously raucous SW winds have grown old & tired. The midpack is well bonded and strong. The November 28 surface hoar is still being found in isolated, sheltered below treeline locations buried 120cm. The deep crust/facet combo from early November still exists but seams to have gone dormant for the time being.

Avalanche Problems

Wind Slabs

NW winds are forecasted to be screaming (extreme) at ridgetop.  Watch for wind slab formation in exposed terrain in both the alpine and treeline vegetation bands.
Avoid freshly wind loaded features.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 4

Persistent Slabs

I suspect this layer will spring back to life when the warm temps and sunshine come out Tuesday. Slopes that didn't slide in the last cycle are of particular concern.  Pull back to simple terrain without overhead hazard as soon as it warms up.
As the sun comes out and the temperatures rise the potential for large avalanches failing on the buried surface hoar will quickly increase.>Avoid traveling on slopes which are becoming wet due to sun and warm temperatures.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 5