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Avalanche Forecast

Mar 21st, 2012–Mar 22nd, 2012
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
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: South Columbia.

Be wary of any slopes receiving direct sun. Solar warming could trigger avalanches or weaken existing slabs.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Thursday: Light snow. 5-10cm. Light to moderate south-west winds. Freezing level valley floor.Friday/Saturday: Clear and sunny. Light winds. Afternoon temperatures rising on sunny slopes, with the freezing level falling to valley floor at night.

Avalanche Summary

On Tuesday, a number of size 1-1.5 avalanches were triggered in the storm snow naturally and by people. The frequency of deep releases on the February persistent weakness has gone down, with the most recent reports occurring at the weekend (size 3-3.5 slabs, 100-180 cm deep). There were also two size 3 avalanches that were triggered accidentally by snowmobilers just south of the region near Kimberley on Sunday. I'm concerned about strong solar warming on Friday and Saturday potentially triggering cornice fall or surface avalanches, which could step down to the Feb weakness, leading to very large releases.

Snowpack Summary

South to south-westerly winds combined with new snow have created wind slabs in the alpine and at treeline. Sunny periods on Sunday developed a sun-crust on southerly aspects up well into the alpine. Older storm snow is reported to be bonding well to underlying surfaces. A key concern is a persistent weak layer of buried surface hoar from mid-February that is buried 1-2 m deep. Snowpack tests give sudden "pops" results on this layer, indicating the ongoing potential for very large avalanches. Because the layer is so deeply buried, it's unlikely to fail without a large trigger (e.g. cornice fall or explosive). However, there's always the chance of someone stumbling across a sweet spot, particularly in shallow snowpack areas.

Avalanche Problems

Wind Slabs

Wind slabs can be found in the alpine and at treeline, behind ridges and terrain breaks. Very large cornices also threaten slopes below.

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 4

Storm Slabs

Storm snow may sluff easily or fail as a slab, especially in steep or convex terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 3

Deep Persistent Slabs

Reports of avalanches releasing on the mid-February weak layer are becoming less frequent. Large triggers like cornice falls may release the slope below, resulting in very large destructive avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Unlikely - Possible

Expected Size: 3 - 9