Avalanche Forecast

Issued: Dec 20th, 2015 4:00PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

Windslabs continue to develop in the alpine. Concern remains for the Dec 3rd persistent weak layer, dig frequently to check for presence of this spotty surface hoar problem and keep a watchful eye on the character of the slab above it. TH

Summary

Weather Forecast

Westerly flow will bring light amounts of precip under mainly cloudy skies with light to moderate alpine winds over the forecast period. Expect 10cm total through Wednesday. Temps will drop a bit from highs near -10 to as low as -25 at treeline overnight Monday corresponding with some clearing and diminished winds that evening.

Snowpack Summary

10 cm of recent snow has added to the faceted slab over the Dec 3 Surface Hoar now 30 to 50cm deep. While significant shears persist on this layer in isolated, shaded and sheltered areas from 1700 to 2150m, the slab above it continues to lose strength. Meanwhile moderate SW winds are steadily building slabs behind prominent features in the alpine.

Avalanche Summary

Reports citing windslabs up to size 2 in the alpine sensitive to skier traffic have come in over the last 24 hrs as well as a few natural cornice events. Small loose dry activity has also been seen at treeline and above, while these are of minimal consequence at this time in all but extreme terrain, their size is likely to increase.

Confidence

Due to the number of field observations

Problems

Wind Slabs

New isolated slabs soft slabs are steadily growing in alpine terrain. These fresh slabs are easily triggered by skiers and will be found in the immediate lee sides of prominent features. Fragile recent cornice growth has also been failing naturally.

Use safe ski cutting techniques before entering ski run. Use caution in lee areas. Recent wind loading has created wind slabs.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

The slab above this layer has facetted out in many areas which has lead to a decrease in triggering however tests continue to produce significant shears. Be cautious in aggressive terrain or in wind affected areas where the slab may retain strength.

Dig down to find and test weak layers before committing to a line.Avoid unsupported slopes.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Dec 21st, 2015 4:00PM