Avalanche Forecast

Issued: Mar 29th, 2013 9:43AM

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

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 increasing.

Summary

Confidence

Good

Weather Forecast

The region continues to be under a significant high pressure system and blocking pattern that will not allow any active weather throughout the forecast period. Sunny skies with few clouds and unseasonable high freezing levels will continue.Saturday: Few clouds. Alpine temperatures near 5.0 and freezing levels rising to 2500 m. Ridgetop winds will blow light from the West.Sunday: Mostly sunny with possible high cloud. Alpine temperatures 4.0 degrees and freezing levels 2600 m. Ridgetop winds will be light from the NW.Monday: Mix of sun and cloud. Alpine temperatures near 0.0 degrees and freezing levels hover around 2200 m. Ridgetop winds blowing light from the West.

Avalanche Summary

Several solar induced cornice releases up to size 3 occurred, not triggering slabs on the slopes below. Numerous loose wet avalanches initiated from solar aspects above 2000 m up to size 2.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. Cornice fall is ongoing. Wind and storm slabs are 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.

Give cornices a wide berth when travelling on or below ridges.>Pay attention to overhead hazards like cornices.>

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

Elevations: Alpine.

Likelihood

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.>Take advantage of cooler parts of the day if you're planning bigger objectives or plan to travel under large avalanche paths.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely - Certain

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 30th, 2013 2:00PM