Avalanche Forecast

Issued: Mar 26th, 2013 9:59AM

The alpine rating is moderate, 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

Mainly clear skies with some high-mid cloud cover and temperatures steadily increasing by the weekend.Wednesday:Â Mix of sun and cloud. Treeline temperatures near -2.0. Freezing levels rising to 1500 m in the afternoon and then falling to 900 m overnight. Ridgetop winds will be light from the SE.Thursday/Friday: Partial cloud cover, then mostly sunny on Friday. Treeline temperatures near -1.0. Freezing levels will ride to 1900 m and then falling back to 300 m overnight. Ridgetop winds will be light rom the SW.

Avalanche Summary

On Monday, numerous loose dry and wet avalanches occurred, mostly from step terrain features. Natural cornice fall up to size 2.0 was also reported. Be aware of continued natural loose wet, or wet slab avalanche activity especially on solar aspects.

Snowpack Summary

Large fragile cornices loom over many slopes. These may become weak and fail due to 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 up to 2000 m, and melt-freeze crusts are forming on solar aspects.Last week's storm snow is settling into a cohesive slab overlying an old crust ( down 50-60 cm) 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.

Problems

Cornices

Solar radiation and warm daytime temperatures, cornices may become unstable. There is a chance the weight of a cornice dropping onto the slope below could trigger an avalanche on the Mid-March crust.

Cornices become weak with daytime heating, so travel early on exposed slopes.>Give cornices a wide berth when travelling on or below ridges.>

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

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 Mid-March crust down 40-60 cm below the surface. It may be more reactive in areas that have been slightly affected by the wind.

Dig down to find and test weak layers before committing to a line.>Plan escape routes and identify safe zones before committing to your line.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 5

Loose Wet

Solar aspects are likely to see loose wet avalanches 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 - 4

Valid until: Mar 27th, 2013 2:00PM