Avalanche Forecast

Issued: Mar 25th, 2013 10:15AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Cornices, Persistent Slabs and Loose Wet.

swerner, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Good

Weather Forecast

A dominating ridge of high pressure will continue over the Interior through the forecast period. Spring-like conditions will remain the theme, with gradual warming Wednesday/Thursday. Tuesday: Mainly clear skies with possible mid-high cloud cover. Freezing levels 1400 m in the afternoon, and then falling back to valley bottom overnight. Ridgetop winds blowing light from the West.Wednesday: Scattered high cloud. Freezing levels 1500 m, and then falling to 800 m overnight. Ridgetop winds light from the South.Thursday: Mostly clear and sunny. Freezing levels 1900 m and then falling to valley bottom overnight. Ridgetop winds will blow light from the SouthWest.

Avalanche Summary

On Sunday, small loose dry/wet avalanches occurred from steeper terrain features. One skier triggered size 1.5 slab avalanche released on a North aspect around 2000 m over a steep convex feature. On Saturday an avalanche fatality occurred in the Hell Roaring riding area located in the eastern ranges of the region. We have very limited information as the investigation is ongoing. At this point it sounds like a size 3 machine triggered slab avalanche. Additionally a skier triggered slab avalanche size 1.5 occurred in the Whitewater area (outside the ski area boundary). This avalanche was triggered from the leeward side of a cross-loaded feature and ran on a buried crust around 1980 m on a North aspect.

Snowpack Summary

20 and 80 cm of last week's storm snow is settling into a cohesive slab overlying a thick crust that exists up to ridge top. The crust appears to have gained some strength in most places, but may still host a poor bond and has been susceptible to skier and rider triggers. A buried surface hoar layer sits approximately 80 cm below the surface and continues to fail in a sudden planar fashion when tested. In some places it may not be a concern due to the thick supportive crust that lies above it. However, it may be more reactive to a trigger from a variable, thin snowpack area or a large trigger like a cornice fall or a snowmobiler.Large fragile cornices loom over many slopes. These may become weak and fail under the influence of the sunshine. Cornice fall can act as a large trigger on slopes below, and may trigger a deeper instability if it exists. Surface snow has become moist, and melt-freeze crusts are forming on solar aspects.

Problems

Cornices

With solar radiation and warm daytime temperatures, cornices will become unstable. There is a chance the weight of a cornice dropping onto the slope below could trigger an avalanche on the March 15th crust.

Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Persistent Slabs

Slab avalanches have been reactive to human triggering. The weak interface being the March 15 crust down 40-60 cm below the surface. It may be more reactive in areas that have been slightly affected by the wind.

Plan escape routes and identify safe zones before committing to your line.>Dig down to find and test weak layers before committing to your line.>Avoid lee and cross-loaded terrain near ridge crests.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 5

Loose Wet

Solar aspects are likely to see loose snow avalanches on solar aspects when the sun comes out and temperatures start to warm. There is a danger that surface avalanches may step down to pull out slabs on the buried crust.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Mar 26th, 2013 2:00PM