Avalanche Forecast

Issued: Jan 16th, 2015 8:23AM

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

rbuhler, Avalanche Canada

Purcells.

New storm problems combined with the persistent slab problem means tricky conditions for the weekend. Use a conservative approach if you are heading into the mountains.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain on Sunday

Weather Forecast

A weak ridge of high pressure will keep the interior dry for Friday night and Saturday morning. Light flurries are expected Saturday afternoon with moderate SW alpine winds. Freezing levels should be at around 1200m. On Sunday, another frontal system will cross the interior bringing 10-15mm of precipitation and moderate-strong SW alpine winds. Freezing levels may reach around 1500m. Lingering flurries are expected for Monday as a ridge of high pressure begins to build over the interior.

Avalanche Summary

On Thursday, explosives triggered a size 2 avalanche. No new avalanches reported on Wednesday. Explosive control on Tuesday produced two size 2 slab avalanches in the deeper western part of the region. These avalanches released on the mid-Dec layer down 90-100cm on steep north aspect slopes. Some natural avalanche activity is possible on Saturday in specific areas including fast sluffing from steep terrain and wind slabs in leeward alpine features. Small avalanches have the potential to step down and trigger a persistent slab which would greatly increase the consequences. Skier triggering is likely in wind loaded areas and steep terrain, and remains possible for persistent slabs where the tricky mid-December layer is still intact.

Snowpack Summary

The new snow has buried widespread 10-20mm surface hoar, a sun crust on steep sun exposed slopes, and/or wind affected surfaces in the alpine. The problematic mid-December surface hoar/crust layer is typically down 40-80cm below the new snow and remains sensitive to human triggering is some areas. The reactivity of this persistent weak layer appears to be quite variable but still has the potential for large, destructive avalanches in some areas. The layer appears to be the most reactive at and below treeline. The mid-Nov weak layer is near the bottom of the snowpack but has generally become inactive.

Problems

Wind Slabs

Soft wind slabs have likely formed in leeward features in the alpine and in isolated areas at treeline.

Use caution in lee areas in the alpine. Recent wind loading have created wind slabs.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

The mid-December weak layer remains problematic at and just below treeline where the snowpack structure may still be primed for human triggering in some areas. The weight of the new snow may increase the reactivity of this layer.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Loose Dry

The new snow sits on a layer of large surface hoar. Fast sluffing from steep terrain may run farther than normal.

Be cautious of sluffing in steep terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 17th, 2015 2:00PM