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Avalanche Forecast

Mar 16th, 2012–Mar 17th, 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
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
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
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: South Columbia.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

Unsettled conditions are expected for Saturday and Sunday. Light winds and convective snow showers are forecast to bring up to 10 cm on Saturday. Clearing overnight should turn to broken skies during the day on Sunday. A ridge of high pressure is expected to bring mostly clear skies on Monday. The freezing level is forecast to be about 1200 metres on Saturday and Sunday, and then lower to about 800 metres on Monday.

Avalanche Summary

Another natural size 4.0 avalanche was reported from the region that may have released on a weak layer of basal facets, or scoured down to the ground once it was in motion. There were also natural size 3.0 avalanches on various aspects in the alpine. Skier controlled avalanches up to size 2.5 were reported, and a couple of skier accidental size 1.0 were also reported.

Snowpack Summary

Moderate precipitation ended around midnight after bringing 15-20 mm of water equivalent. The freezing level went up to about 1400 metres during the storm, so snowfall amounts vary by elevation. The recent series of storms have developed a storm slab that is about 100 cm thick. The storm slab is sitting on a mix of old hard windslabs and crusts. There is a persistent weak layer (PWL) of buried surface hoar from mid-february that is buried between 100-200 cm that is the main concern. This PWL shears with a fracture character that promotes wide propagations that result in very large avalanches. Recent avalanches up to size 4.5 have exceeded historical avalanche paths and resulted in the demolition of old timber.

Avalanche Problems

Persistent Slabs

There are several layers of buried surface hoar in the regions snowpack. The mid-February layer is buried between 100-200 cm below the surface. Avalanches on this layer have produced very wide propagations, and have released from low angle terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 3 - 8

Wind Slabs

Recent windslabs may take a couple of days to settle and bond. Windslab avalanches may trigger persistent weak layers that are buried deeper in the snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 2 - 5

Storm Slabs

Recent snowfalls have combined to build a thick blanket of storm snow. Avalanches that start in the storm snow may step down to one of the persistent weak layers. Solar warming may cause natural activity.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 2 - 6