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Archived

Avalanche Forecast

Mar 3rd, 2012–Mar 4th, 2012
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
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
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 - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

The next wave of the storm is focused on the Central Coast region around Bella Coola. Areas to the north are not expected to get more than about 10 cm on Saturday night, and another 5 cm by noon Sunday. The freezing level is expected to rise to about 700 metres on Sunday and then drop down to the valley bottoms by Monday morning. There is a chance of some convective flurries on Monday before the weak ridge of high pressure brings drier conditions. The next Pacific frontal system is forecast for Tuesday. Expect heavy precipitation and strong westerly winds with a rising freezing level.

Avalanche Summary

A couple of glide slab avalanches were reported up to size 2.5 from steep rock faces that are not suitable for recreation. Some sloughing has been reported up to size 1.5 from lower elevation terrain. Observations have been limited due to poor visibility.

Snowpack Summary

The region received about 10-20 cm overnight and into Saturday morning. Moderate westerly winds created new windslabs in the alpine and at treeline. There are some older windslabs on south through southwest aspects that may be stripped by the new wind or cross-loaded. There is between 70-100 cm of snow above the buried weak layer of decomposed and fragmented crystals that has been giving moderate shears in stability tests. Some areas are reporting a buried surface hoar from early February that is buried at the same depth. The weak layer may be triggered by light additional loads at treeline and below. This interface is variable, it consists of a strong melt freeze crust below 1000m, above 1000 m exists facets, surface hoar (in more sheltered areas), sun crust or wind press. The surface hoar is not widespread but is responsible for much of the larger avalanches that occurred earlier this week. Areas below treeline are quite variable. There are spring like conditions with a melt-freeze crust in some areas, and others are still experiencing winter at lower elevations.

Avalanche Problems

Wind Slabs

New snow and strong westerly winds are developing new windslabs that may fail naturally or be easy to trigger with light additional loads.

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 2 - 5

Persistent Slabs

The new storm is expected to add a new load above the persistent weak layer of facets, surface hoar and crusts that are buried down about 70 cm. Avalanches that start in the storm snow may step down and cause large destructive avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 6