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Archived

Avalanche Forecast

Mar 9th, 2012–Mar 10th, 2012
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
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
4: High
The avalanche danger rating below treeline will be high

Regions: South Coast.

Very dangerous avalanche conditions exist at this time.

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Friday night: Around 5 cm new snow expected to fall, with freezing levels around 1000 m and SW winds gusting 60-80 km/h. Saturday: Light precipitation, ramping up in the afternoon, with 10-15 cm new snow anticipated by the end of the day. Moderate southwest winds are expected with freezing levels around 1000 m. Sunday: An additional 15-20 cm new snow is expected by the end of the day. Winds strong southwesterly. Freezing levels staying around 1000m. Monday: Another, more intense storm system arrives, bringing 30-40 cm new snow, temperatures cool enough for snow at most elevations and high winds.

Avalanche Summary

On Friday, the newly-forming storm snow could be easily triggered by ski-cutting at alpine elevations. On Thursday, widespread activity to size 2.5 was reported from the Coquihalla in response to warm temperatures. A size 2 avalanche was reported from Mt Rohr on a southerly aspect at 2000 m. Tuesday's reports from Duffey Lake and Chilcotin areas suggest that a persistent facet/crust weakness is very touchy in treeline gullies and below treeline cutblocks. Several Size 2.0-2.5 persistent slabs, including multiple sympathetic releases, were skier-triggered in treeline features (gullies) and below treeline cutblocks. More reports of last weekend's widespread large natural avalanche cycle are coming in with observations of Size 4.5 avalanches. Some of the larger slabs propagated 2-3Km along ridgelines and stepped down to the mid-February persistent weakness, and there's no reason why similar avalanches can't happen with this next round of loading.

Snowpack Summary

Strong and variable winds in exposed treeline and alpine areas have resulted in reverse loading, widespread surface crusts, and looming undermined cornices. In the Duffey Lake and Chilcotin regions south aspects are described as spooky with a very hollow feeling with a couple of different poorly-bonded crusts in the upper snowpack. The lower weakness, comprising surface hoar, facets and a crust, is down 60-80cm at treeline and over a metre at higher elevations. It is touchy on all south aspect slopes as well as on slopes of all aspects at treeline and below. In the Cascades, 70-100cm of recent storm snow combined with five straight days of sustained extreme winds created a highly unstable wind and storm slab problem that could easily re-awaken with additional loading by new snow.

Avalanche Problems

Persistent Slabs

Continued diligence and conservative decisions are necessary. The potential for cornice triggers, remote triggering, step down avalanches, and wide propagations makes this problem particularly tricky to manage.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 4 - 8

Wind Slabs

Strong SW winds are setting up fresh wind slabs on mainly N to E aspects. Previous wind slabs still exist on a variety of aspects. Cornices are large and will build further with the forecast weather.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Very Likely

Expected Size: 2 - 5

Storm Slabs

Touchy weaknesses within and under the recent storm snow are expected to become reactive with additional snow load. Old storm slabs from last week could easily wake up again, increasing the magnitude of potential occurrences.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 3 - 6