Avalanche Forecast

Issued: Mar 24th, 2014 8:46AM

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

Peter, Avalanche Canada

Purcells.

It's 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

Tuesday: Mainly cloudy with showers or flurries – 5-10 cm. The freezing level should climb to around 1800 m. Ridge winds are light to moderate from the S-SW. Wednesday: Cloudy with flurries – 5-10 cm. The freezing level is around 1500 m and ridge winds are light to moderate from the W-SW. Thursday: Cloudy with flurries. The freezing level is around 1400 m and ridge winds are light.

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.

Snowpack Summary

15 - 25 cm of light density snow has fallen over the last few days. This snow is settling nicely and likely being formed into soft wind slabs immediately lee of ridge crest.Numerous crust 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 70 to 95cm 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 100 - 180cm, seams 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. It continues to produce large destructive natural avalanches every few days. 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. Watch for triggering in gullies, and in the lee of terrain breaks and ridge crests.

Extra caution needed around cornices with current conditions.>Use ridges or ribs to avoid pockets of wind loaded snow.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

There are a number of persistent layers in the mid to upper snowpack which have professional operators concerned. These layers, which include recently buried crusts and surface hoar, continue to produce sudden failures in snowpack tests.

Use conservative route selection, stick to moderate angled terrain with low consequence.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Deep Persistent Slabs

The deeply buried early February interface should stay on your radar as activity on this layer would be large and destructive. Possible triggers include cornice fall, thin spot triggering 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

3 - 6

Valid until: Mar 25th, 2014 2:00PM