Avalanche Forecast

Issued: Dec 13th, 2013 8:25AM

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.

ccampbell, Avalanche Canada

Purcells.

New snow, wind, and warm temperatures will drive the avalanche hazard over the weekend.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Saturday: Cloudy with flurries expected to bring no more around 5cm of new snow. Freezing levels expected to remain at or near valley bottoms with treeline temperatures around -2. Ridge top winds are expected to be moderate westerlies. Sunday: Moderate snowfall with 10-15cm of accumulation, freezing levels rising up to 1800m and strong southwesterly winds. Monday: Light snowfall with less than 5cm of accumulation, freezing levels around 1500m and strong westerly winds.

Avalanche Summary

Reports from yesterday are limited to a few loose sluffs from steep terrain. On Tuesday, a wind slab avalanche size 1.5 was easily triggered under the weight of a rider from a NE aspects.

Snowpack Summary

Light incremental snowfall is starting to bury surface hoar and a faceted upper snowpack. Snowpack depths at treeline seem to vary from 70 - 110 cm with high variability in wind-exposed areas. A persistent weakness of buried surface hoar and facets, with an associated crust, is down approximately 20-40cm . Recent reports suggest this layer has been producing variable results with snowpack tests, but it may become reactive as a cohesive slab develops with warming and/or additional load. The base of the snowpack is made up of weak facets and depth hoar. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on a steep, convex slopes.

Problems

Wind Slabs

Deep and touchy winds slabs are lurking below ridge crests and behind terrain features on lee and cross-loaded slopes. Expect wind slab development to continue for the forecast period.

Be cautious as you transition into wind affected terrain.>Avoid freshly wind loaded features.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

Persistent weakness may become more touchy with forecast warming and additional load from new snow and wind. This includes mid-pack surface hoar (more of a concern in deeper snowpack areas), and basal facets (more of a concern in shallow areas).

Whumpfing is direct evidence of a buried instability.>Dig down to find and test weak layers before committing to a line.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Dec 14th, 2013 2:00PM