Avalanche Forecast

Issued: Mar 28th, 2013 10:53AM

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

swerner, Avalanche Canada

Purcells.

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 and very warm temperatures during the day. Some cooling will exist overnight. 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 2300 m in the afternoon then dropping Â 1000 m overnight. Ridgetop winds will blow light from the West.Saturday: Few clouds. Alpine temperatures reaching 5.0 degrees. Freezing levels rising to 2500 m in the afternoon then dropping to 1400 m overnight. Ridgetop winds blowing light from the West.Sunday: Mostly sunny. Alpine temperatures -2.0. Freezing levels 2000 m Â and then falling to valley bottom overnight.

Avalanche Summary

On Wednesday,Â numerous solar induced cornice releases up to size 2 occurred and triggered slab avalanches on the slopes below. Some loose wet and dry avalanches initiated from steeper solar aspects.Expect this type of avalanche activity to persist through the forecast period.

Snowpack Summary

Surface faceting and surface hoar growth (up to 20 mm) has been prevalent on shady slopes and at upper elevations, while the surface snow on sun-exposed slopes and at lower elevations has been subject to daily melt-freeze cycles.Cornices are reported to be very large and weakly bonded. Wind and storm slabs are reported to be strengthening, but may continue to be sensitive to human-triggers. The weak layer of buried surface hoar sitting on a crust down around 70-120cm, and has been producing variable but sudden results in snowpack tests. This deep persistent weakness remains a concern because of the potential for very large avalanches particularly with heavy triggers such as cornice falls. Old deep persistent weaknesses, including basal depth hoar, are a concern in shallow snowpack areas.

Problems

Cornices

Natural cornice falls are a concern during daytime warming. Cornices may also be triggered easily by traveling near them. Slopes with corniced entrances, or exposed to cornice falls should be avoided with these conditions.

Cornices become weak with daytime heating, be aware of your overhead hazards.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 5

Persistent Slabs

Small solar triggered slides, cornice fall, or thin-spot triggering may overload a persistent weakness buried near 100 cm deep. This could lead to surprisingly large avalanches. Wind slabs linger on lee slopes and cross-loaded terrain features.

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: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Loose Wet

Expect to see wet loose snow avalanches out of steep rocky sun-exposed slopes. Natural avalanche activity. snowballing, moist and wet snow surfaces are all initial indications of the upper snowpack deteriorating.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely - Certain

Expected Size

1 - 4

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