Avalanche Forecast

Issued: Jan 15th, 2015 8:06AM

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

rbuhler, Avalanche Canada

South Columbia.

Storm conditions will create new problems for the weekend but don't forget about the tricky persistent slab problem. Large, destructive avalanches remain possible.

Summary

Confidence

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

Weather Forecast

The cold front passes over the interior regions on Friday and should be finished by Friday evening. The South Columbia region can expect 10-15mm of precipitation with freezing levels of 1000-1200m. Alpine winds are expected to be strong from the SW but may switch to NW at the tail of the storm. On Saturday, light precipitation (1-3mm) is forecast with freezing levels around 800m and moderate SW alpine winds. The next frontal system is expected for Sunday and is forecast to bring another 10-15mm of precipitation.

Avalanche Summary

On Wednesday, explosives triggered a cornice but the cornice did not trigger a slab. On Tuesday, a natural size 2.5 persistent slab was reported. This released on the mid-Dec weak layer. Sluffing from steep sun exposed slopes was also reported. Some natural avalanche activity is expected on Friday 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 snowfall is burying widespread 10-20mm surface hoar up, 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 80-120cm 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.

Problems

Wind Slabs

New snowfall combined with strong SW winds will result in new wind slab formation on Friday.

Use caution in lee areas in the alpine and at treeline. Wind loading will quickly form new wind slabs.>

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

Elevations: Alpine, Treeline.

Likelihood

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.

Use conservative route selection, stick to moderate angled terrain with low consequence.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

3 - 6

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

Likely

Expected Size

1 - 2

Valid until: Jan 16th, 2015 2:00PM