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Archived

Avalanche Forecast

Dec 12th, 2012–Dec 13th, 2012
Alpine
4: High
The avalanche danger rating in the alpine will be high
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
4: High
The avalanche danger rating in the alpine will be high
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
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

Regions: Northwest Coastal.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

A series of frontal systems will affect the coast for the next few days. The timing is a bit uncertain but the general pattern is stormy.Thursday: Strong W winds. Alpine temp -4. Moderate snow (locally heavy).Friday: Moderate to strong W winds. Alpine temp -6. Light to moderate snow.Saturday: Light winds. Alpine temp -10. Moderate to heavy snow.

Avalanche Summary

A natural cycle occurred on Tuesday with avalanches to size 2.5 running in steep terrain at treeline and alpine elevations. Explosives testing produced several very large (size 3-4) slabs on northerly aspects near Stewart. These failed on basal facets and/or glacial ice and were up to 4 m deep and 250-300 m wide. Recent storm/wind slabs above 1600 m which were triggered by cornice fall or explosives also stepped down to basal facets. Low elevation steep terrain was also shedding numerous small, moist loose avalanches during Tuesday’s warming.

Snowpack Summary

Storm snow instabilities are likely for the next few days. New and buried wind slabs are widespread and exist on a variety of alpine and exposed treeline slopes due to variable winds. A rain crust is now buried by new snow at low elevations. A November facet/crust layer can be found near the base of the snowpack. Very large releases are still occurring on this layer with a heavy trigger, such as storm slabs stepping down, explosives, or cornice fall.

Avalanche Problems

Storm Slabs

Storm slabs are likely to be encountered on many slopes. Be alert for new and buried wind slabs behind ridges and ribs. Storm/wind slabs could step down to trigger a persistent weakness.
Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Travel one person at a time on all slopes capable of producing an avalanche.>Travel in avalanche terrain is not recommended without advanced training and extensive experience.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 5

Deep Persistent Slabs

A deeply buried facet/crust weakness exists. Very large and destructive avalanches are possible, and may be triggered by  heavy loads such as cornice fall or a storm slab stepping down.
Do not travel on slopes that are exposed to cornices overhead.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 8