Avalanche Forecast

Issued: Dec 14th, 2012 9:00AM

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

pmarshall, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Track of incoming weather is uncertain

Weather Forecast

Synopsis: A series of weakened frontal systems will affect southern interior over the next few days. The strongest system is forecast to affect the region on Monday.Saturday: Light snow – 5-10 cm. Winds should be moderate from the SW. The freezing level should remain near valley bottom. Sunday: Lingering flurries with snow possibly developing overnight. Winds remain moderate from the W-SW. Freezing level near valley bottom. Monday: Moderate snow. Freezing level could jump to 800 m.

Avalanche Summary

A few small soft slabs were skier triggered on East and South aspects, and several small loose snow avalanches were reported in steep terrain. An older (approximately from Dec. 10th) natural slab avalanche size 2.5 was also observed on an East facing windloaded convex slope. The crown was an average of 60 cm deep. There was also multiple releases from explosives that ran in the new snow from North West to South East facing slopes.

Snowpack Summary

Wind slabs remain a concern in exposed lee terrain in the alpine and at treeline. The new snow is also burying some older deeper windslabs on northerly aspects in the alpine. Overall, the upper snowpack is reported to be settling well. The November 28 surface hoar down 100-140 cm (between 1500 and 2000 m) is producing moderate to no results in snowpack tests. The early November crust, down 150-200 cm, has produced occasional sudden results in snowpack tests. Professionals are still cautious about these lingering persistent slab problems, but the likelihood of triggering continues to decrease as the overlying snowpack builds and continues to gain strength.

Problems

Wind Slabs

Weak wind slabs are likely in exposed lee terrain and cross-loaded gullies, and may be triggered by the weight of a skier or snowmobile.

Avoid lee and cross-loaded terrain near ridge crests.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

A weak layer of surface hoar is buried down about 100 cm. Avalanche activity has been sporadic on this weakness, but smaller slides could step down and create large avalanches.

Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Dec 15th, 2012 2:00PM