Avalanche Forecast

Issued: Dec 21st, 2015 7:56AM

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

jlammers, Avalanche Canada

Purcells.

The wind effect from the last storm seems to be highly variable. The best (and safest) riding may be found on sheltered slopes at treeline and below.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A fairly benign weather pattern is setting up for the forecast period. Light flurries are expected for Tuesday, but snowfall amounts shouldn't exceed 3cm. Isolated flurries with occasional sunny breaks are forecast for Wednesday and Thursday. Ridgetop winds are forecast to remain mainly light for all 3 days while alpine temperatures should hover between -12 and -15.

Avalanche Summary

Observations were limited on the weekend, although touchy wind slab avalanches to 20cm in depth were being triggered near ridgetop in response to new snow and wind in the north of the region. I'd anticipate the possibility of human-triggered wind slab avalanche activity over the next few days.

Snowpack Summary

Throughout last weekend there was up to 20cm of new snow. Strong southerly winds have redistributed much of this snow into deeper wind slabs in exposed lee features in the alpine and at treeline. Between 40 and 80cm below the surface you'll likely find a layer of weak buried surface hoar which is most prominent between 1400m and 1800m although it may extend higher in the mountains south of Invermere. Snow pit tests suggest that human triggering of this interface is becoming unlikely, although a release at this interface could be destructive in nature.

Problems

Wind Slabs

Recently formed wind slabs should strengthen gradually over the next few days. While that happens, I'd stick to sheltered lower elevation slopes where the riding is better (and safer).

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Be cautious as you transition into wind affected terrain.>Be alert to conditions that change with elevation.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

A layer of buried surface hoar can be found between 1400m and 1800m. Although this layer has become less likely to trigger, I'd remain cautious on steep roles in cut-blocks and open glades below treeline.

Conditions are greatly improved, but be mindful that persistent weak layers are still present.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Dec 22nd, 2015 2:00PM