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Avalanche Forecast

Dec 22nd, 2014–Dec 23rd, 2014
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
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: Northwest Coastal.

New storm snow with strong winds will quickly increase the hazard on Tuesday.

Confidence

Fair - Due to the number of field observations

Weather Forecast

A frontal system is expected to bring around 15-20mm of precipitation to the North Coast on Tuesday. Another 10-20mm is possible Tuesday night into Wednesday morning. Freezing levels on Tuesday are expected to be 800-1000m with strong-to-extreme winds from the SW in the alpine. On Wednesday, precipitation should taper off in the morning with freezing levels around 500m and winds easing to moderate NW in the alpine. Christmas day looks to be a mix of sun and clouds with freezing levels around 500m and moderate winds in the alpine.

Avalanche Summary

Reports from Sunday of natural storm slab avalanches up to size 2.  These were typically 15-30cm thick slabs but the thickest reported was 70-80cm.  Typical start zone elevations were 1400-1500m. Explosive control also produced numerous storm slab avalanches with the same characteristics.  I expect we will see more natural storm slab activity on Tuesday.

Snowpack Summary

A storm slab developed over the weekend that is about 50-70 cm thick at higher elevations. Strong Southwest winds have transported snow into windslabs that may be about 100 cm thick. Rain up to about 800-900 metres elevation may have resulted in loose wet avalanches where that rain fell on snow from earlier in the storm. Cornices are expected to be large and fragile due to new rapid growth. Deeper in the snowpack, weaknesses such as the mid-November crust-facet layer still exist. Avalanches at this interface have become unlikely, although the consequences of a release remain high. This layer may be more sensitive to triggering in steep, unsupported high alpine terrain, or in the far north of the region.

Avalanche Problems

Storm Slabs

The new storm snow is adding to the storm loading from the weekend. These storm slabs are likely sitting on a weak layer of buried surface hoar. Strong winds are loading leeward slopes in exposed terrain and have created large cornices.
Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 4