Avalanche Forecast

Issued: Feb 14th, 2015 7:51AM

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

pgoddard, Avalanche Canada

Purcells.

A Special Public Avalanche Warning is in effect for this region.

Summary

Confidence

Fair

Weather Forecast

The next three days look cool and dry, with sunny spells. The freezing level is around 1400 m on Sunday, falling to valley floor overnight as a strong ridge sets up. It is expected to get into a diurnal cycle after that (falling to valley floor at night and rising by day to around 1200 m). Winds are generally light from the NW.

Avalanche Summary

A couple of large naturally-triggered slabs were observed on Friday in response to warming. One was a size 3 on a west aspect at around 2500 m. Size 2 avalanches were also observed on NE aspects. On Thursday, a size 2 natural avalanche was observed on a north-facing slope. Explosives also triggered numerous size 2-3.5 avalanches up to 2 m deep, some of which ran at ground. Large cornice falls were also observed. On Wednesday, a skier took a ride in a size 2 persistent slab which failed on the mid-Jan layer in the Dogtooth range. As temperatures cool this weekend, conditions should gradually improve, but large avalanches remain possible, and sun may cause another spike in avalanche activity on steep solar aspects.

Snowpack Summary

As the weather finally cools after ten days of very warm temperatures and bursts of rain, surface crusts are likely to form. Underneath newly formed crusts, you may find moist snow for a few days yet. At alpine elevations, new wind slabs or storm slabs may be found. Cornices may be large and weak. The late-Jan crust/surface hoar layer is 1-2 m deep in the west, and can be found within the upper metre of the snowpack further east. It is variably reactive and still the main concern in many areas. The mid-January surface hoar, deeper again, remains problematic in some areas. The mid-December weak layer may still be on the radar in isolated areas in the east. The mid-November weak layer of crusts and facets can still be found near the bottom of the snowpack. It seems to have been reawakened with warming and has been triggered by explosives over the last few days, taking the entire snowpack with it.

Problems

Persistent Slabs

Persistent slabs are most likely to be triggered from thin snowpack areas, or with large triggers like cornice fall or an avalanche stepping down.

Use conservative route selection; stick to moderate angled terrain with low consequence.>Avoid common trigger points like convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Wind Slabs

Wind slabs may be lurking on lee and cross-loaded features in the alpine. Cornices are weak and may collapse.

Be cautious as you transition into wind affected terrain.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Loose Wet

Direct sun may weaken the surface layers, leading to a spike in avalanche activity on steep solar aspects.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

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

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Feb 15th, 2015 2:00PM