Avalanche Forecast

Issued: Mar 29th, 2012 10:11AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Wind Slabs, Storm Slabs and Cornices.

mpeter, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Friday: Continued stormy conditions, with strong, gusty southwesterly winds and freezing levels reaching 1500m. 10-15cm is possible. A ridge should build late in the day giving clearing skies overnight. Saturday: A mix of sun and cloud, with moderate, gusty southwest winds. Some convective flurries are possible with accumulations over south and west facing terrain. Freezing levels could reach 1400m. Sunday: Expect unsettled skies with flurries possible. Southwest winds ease to light values and freezing levels should be slightly lower.

Avalanche Summary

Natural, explosive and human triggered avalanches have been reported up to size 2.0, with all failures on the March 26 interface. At lower elevations (where the surface is moist) these are running as loose events and at higher elevations the new snow is propagating as a slab.

Snowpack Summary

Above 2000m, 20-40cm of new snow now overlies the March 26 interface. This has been accompanied by consistently moderate and at times gusty southwesterly winds forming windslabs in lee locations. Cornices loom, and will continue to grow with this weather pattern. The March 26 interface is a crust on all aspects except true north treeline and alpine, where small surface hoar (5mm) is present in sheltered places. The bond between the new snow and this interface is weak, especially where the surface hoar is present. At lower elevations, the high freezing levels have made the new snow heavy and moist. The deep, persistent early February surface hoar lingers in the snowpack giving sudden results in testing. Concern remains with heavy triggers and rapid loading.

Problems

Wind Slabs

The increased wind and new snow are forming windslabs in lee zones at ridgecrest. These overlie a slick melt freeze crust in most locations and surface hoar on North aspects. A small windslab event could step down to the deep, persistent weakness.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Storm Slabs

The new snow is bonding poorly to the March 26 interface. At lower elevations, expect moist sluffing, while higher up (drier snow) the storm slab is more cohesive. A small storm slab event (or sluff) could step down to the deep weaknesses.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Cornices

Cornices are very large and will grow under the current conditions. There is potential for triggering deep persistent slabs on underlying slopes.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 7

Valid until: Mar 30th, 2012 9:00AM