Avalanche Forecast

Issued: Mar 30th, 2013 9:56AM

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

swerner, Avalanche Canada

Purcells.

Danger could INCREASE TO CONSIDERABLE with intense radiation on south and west aspects, especially at treeline and below. Be aware of how the warm weather is changing the snowpack.

Summary

Confidence

Good

Weather Forecast

A dominating high pressure system with sunny skies, rising freezing levels and light winds continues through to Monday. The pattern will start to deteriorate by Tuesday, showing increased cloud and grey skies with no precipitation. Sunday: Few to scattered high cloud. Alpine temperatures 4.0 and freezing levels 2600 m. Ridgetop winds light from the NW.Monday: Scattered clouds. Alpine temperatures 5.0 and freezing levels rising to 2600 m. Ridgetop winds blowing light from the NW.Tuesday: Cloudy. Alpine temperatures -1.0 and freezing levels falling to 2300 m. Ridgetop winds blowing light from the SW.

Avalanche Summary

Numerous natural loose wet avalanches up to size 1.5 and one natural cornice fall size 2.5, not pulling a slab on the slope below.

Snowpack Summary

Surface faceting and surface hoar growth (up to 20 mm) has been prevalent on most aspects and elevations, while the surface snow on sun-exposed slopes and at lower elevations has been subject to daily melt-freeze cycles.Cornices are large and weak. Pockets of wind slab can be found on lee slopes and possible to trigger under your skies or sled. A layer of buried surface hoar sitting on a crust down around 70-120cm, and has been producing variable results in snowpack tests. This 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, 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.

Likelihood

Likely - Very Likely

Expected Size

2 - 5

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.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 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.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Mar 31st, 2013 2:00PM