Avalanche Forecast

Issued: Mar 27th, 2014 9:15AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Wind Slabs and Deep Persistent Slabs.

mbender, Avalanche Canada

Purcells.

It is still possible to trigger large persistent slab avalanches throughout most of the region. Dealing with this type of problem requires discipline to stick to conservative decision making, even when no obvious signs of instability are observed.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Friday: Cloudy with isolated flurries. Winds light southwest. Freezing level rising to 1500m.Saturday: Light to locally moderate snowfall overnight Friday into Saturday. Freezing level 1600m. Winds light southwest.Sunday: Cloudy with scattered flurries. Freezing level rising to 1800m.

Avalanche Summary

Recent reports from the central part of the region (where the most recent snowfall was intensified) indicate natural and explosives triggered avalanches running in the alpine to size 2.5 on all aspects. These were isolated to the most recent storm snow.A size 3 accidentally skier triggered avalanche was reported last Sunday. This avalanche occurred on a steep west-facing alpine slope and stepped down to the ground (up to 2.5 m deep). One person was buried but was recovered without serious injury. On Saturday an anomalous sized 3.5 avalanche released naturally out of a SE facing feature at 2700m in the central portion of the region. Another skier triggered size 2 avalanche was reported on Tuesday. This was in the northern part of the region at 2300m on a northwest aspect, failing on facets near the base of the snowpack.

Snowpack Summary

5-40cm of new snow has fallen in the region (5-10 in the north and up to 40 in the central). This new snow is settling and likely being formed into soft wind slabs immediately lee of ridge crests.Numerous crusts can be found in the upper 60cm of the snowpack on south facing slopes.Â The March 15 crust/surface hoar interface is down 50-80cm. Down90-120cm below the surface you may find surface hoar and crusts buried at the beginning of March. This interface is still touchy in some areas, particularly in the north of the region. It also continues to produce sudden planar failures in compression tests.The deeper facet/crust persistent weakness buried at the beginning of February, now down 120 - 200cm, still seems to be reactive and should not be trusted. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive.Â Weak basal facets exist in many areas, but without a large load, triggering is unlikely.

Problems

Wind Slabs

Recent accumulations have likely been blown into pockets of wind slab by generally moderate southwest winds.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>Stay well to the windward side of corniced ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

There are a number of persistent layers in the mid to lower snowpack which have professional operators concerned. Possible triggers include cornice fall, thin spot triggering and/or solar warming.

Be aware of the potential for large, deep avalanches.>Avoid convexities or areas with a thin or variable snowpack.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Mar 28th, 2014 2:00PM