Avalanche Forecast

Issued: Mar 28th, 2013 10:36AM

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

swerner, Avalanche Canada

Kootenay Boundary.

The region will be under the influence of a major warm-up through the weekend. Be aware of snow conditions changing quickly and avalanche danger rising.

Summary

Confidence

Good

Weather Forecast

Spring-like conditions persist through the weekend with clear sunny, very warm temperatures during the day, then cooling at night. Alpine temperatures are expected to reach above zero degrees and little wind is forecast.Friday: Few clouds. Alpine temperatures reaching 4.0 degrees. Freezing levels rising to 2200 m in the afternoon then dropping 800 m overnight. Ridgetop winds will blow light from the West.Saturday: Few clouds. Alpine temperatures reaching 5.0 degrees. Freezing levels rising to 2400 m in the afternoon then dropping to 1000 m overnight. Ridgetop winds blowing light from the West.Sunday: Mostly sunny. Alpine temperatures -2.0. Freezing levels 1600 m and then falling to valley bottom overnight.

Avalanche Summary

On Wednesday, numerous loose wet avalanches up to size 2 were reported East through West aspects at all elevations.from Be aware of overhead hazards such as cornice fall. It is likely that natural loose wet, or wet slab avalanche activity will persist through the weekend.

Snowpack Summary

Large cornices loom over many slopes. Cornice fall can act as a large trigger on slopes below, and may trigger a deeper instability if it exists. The upper 10 cm of surface snow has become moist up to 2300 m, and melt-freeze crusts exists on solar aspects. On Northerly aspects surface hoar (up to 12 mm) and surface facetting is occurring.A cohesive slab overlies an old crust (down 50-60 cm) which exists up to ridge top. The crust appears to have gained some strength in most places, and some test results are showing resistant planar fracture characteristics. This layer may be harder to trigger, but should remain on your radar. It may be triggered by larger loads or skiers or riders hitting the sweet spot from a thinner snowpack area. With the weekend warm-up, wet slab avalanches may initiate naturally on this crust. Deeper down, another buried surface hoar layer sits approximately 80 cm. In some places it may not be a concern due to the thick supportive crust that lies above it. Because snowpack variability exists, it is important to dig down and test weak layers before diving into your line.

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.

Extra caution needed around cornices with current conditions.>Avoid areas with overhead hazard.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 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

Very Likely - Certain

Expected Size

1 - 4

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.

Be aware of thin areas that may propagate to deeper instabilites.>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

Unlikely - Possible

Expected Size

2 - 6

Valid until: Mar 29th, 2013 2:00PM