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Archived

Avalanche Forecast

Dec 27th, 2011–Dec 28th, 2011
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
4: High
The avalanche danger rating below treeline will be high
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
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: Kootenay Boundary.

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Tuesday night: 20-30cm. Wednesday: 5-15cm. Freezing level rising to 1500m. Strong south-west winds. Thursday: Moderate snow. Strong south-west winds. Friday: Generally drier conditions. Weather forecasters have low confidence at the moment (read more in the Forecaster's Blog). Be prepared for local variations in weather, and assume the avalanche danger is elevated in areas with enhanced snow, rain or wind.

Avalanche Summary

A natural and skier-triggered avalanche cycle with slabs up to size 2 was observed over the last couple of days. These were failing on the mid-December surface hoar on north through east aspects from 1700m to the peaks. Wind loading from the south-west overnight Sunday led to naturally-triggered wind-slabs on lee slopes on Monday morning. Touchy conditions are likely to continue through the forecast period and avalanches are likely to increase in size as snow-loading builds.

Snowpack Summary

Up to 30cm of new snow has been redistributed by westerly winds into touchy wind-slabs on lee slopes. Two buried surface hoar layers are causing concern in the upper snowpack. The most recently buried of these is only about 10-15cm deep but is reactive in snowpack tests. The second, a buried surface hoar layer from mid-December around 30-40cm down is now highly reactive, with enough snow above it to put it in the prime range for human-triggering (especially in areas which have received enhanced snowfall. It may take a little bit longer for the Rossland Range to get to this point). It is well-preserved with 10-15mm crystals and is most reactive well below ridges in protected terrain. The mid-pack is generally well settled. Facets exist at the base of the snowpack.

Avalanche Problems

Persistent Slabs

People are reporting a buried surface hoar layer to be highly reactive, with whumphing, cracking and some avalanche activity observed. As snow and wind-loading continue, I expect the size and number of avalanches to increase.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 5

Wind Slabs

Be alert for wind slabs below ridge crests, behind terrain features, and in cross-loaded gullies.

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 3