Avalanche Forecast

Issued: Mar 26th, 2014 9:44AM

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. This type of problem requires discipline and conservative decision making, even if you do not observe signs of instability.

Summary

Confidence

Fair - Freezing levels are uncertain

Weather Forecast

Thursday: Cloudy with flurries. The freezing level 1400 m and light ridge winds. Freezing level at 1400m.Friday: Cloudy with light snowfall expected. Freezing level 1600m. Winds light south. Freezing level rising to 1600m.Saturday: Light to locally moderate snowfall overnight Friday into Saturday. Freezing level 1700m. Winds light south.

Avalanche Summary

Recent avalanche activity has been limited with many areas reporting no new avalanches in the past several days. However, when we do hear reports they are often of large avalanches stepping down to deeply buried persistent weak layers, or even the ground. A size 3 accidentally skier triggered avalanche was reported on 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

Up to 40 cm of snow has fallen over the last few days. Warm temperatures have turned the snow surface moist up to 1700m. Recent moderate winds have formed wind slabs in the lee of ridge crests.Numerous crusts can be found in the upper 30 cm of the snowpack on south facing slopes. These crusts produce sudden collapse failures in snowpack tests. A moderate shear persists down 30 - 50cm on the March 15 crust/surface hoar interface. Down 90 to 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, seems to be more active in this region than any other in the province and is still very difficult to trust. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive. 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.>Extra caution needed around cornices with current conditions.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

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.

Avoid convexities or areas with a thin or variable snowpack.>Be aware of the potential for large, deep avalanches.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Mar 27th, 2014 2:00PM