Avalanche Forecast

Issued: Dec 26th, 2013 8:24AM

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

jlammers, Avalanche Canada

South Rockies.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Friday: Light flurries / Moderate southwest winds with extreme gusts / Freezing level at 1300mSaturday: Mix of sun and cloud / Light winds / Freezing level at 900mSunday: Overcast skies / Light winds / Freezing level at valley bottom

Avalanche Summary

On Christmas Eve a backcountry skier triggered a size 2 slab avalanche on an alpine slope in the Harvey Pass area. The slab was reportedly 70cm deep and 150m wide and was thought to have slid on the late-November crust/facet interface. There were no reported injuries with the avalanche.

Snowpack Summary

There appears to be a lot of snowpack variability across the region. Snowpack depths at treeline seem to vary from 60 - 130 cm with high variability in wind-exposed areas. Mostly modest amounts of low density snow have fallen over the last week and have likely been shifted into small wind slabs in exposed areas. Located just below the surface is a layer of weak faceted crystals which formed during the cold snap at the beginning of December. At this point, there does not seem to be enough of an overlying slab to create a widespread problem. In the mid pack is the late-November/early-December interface which is made up of surface hoar, a crust, and/or facets. This layer is typically down 30-70cm and has reached the tipping point for rider triggering in a few areas including the Harvey Pass area. Check out this video of a recent snowpack test on this layer.

Problems

Persistent Slabs

A skier-triggered size 2 avalanche in the Harvey Pass area indicates persistent weaknesses buried at the end of November have become active. The variable nature of this instability requires an investigative approach for safe mountain travel.

Make observations and assess conditions continually as you travel.>Dig down to find and test weak layers before committing to a line.>Avoid shallow snowpack areas on steep, convex terrain where triggering is more likely.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 4

Wind Slabs

Recent strong winds have redistributed loose surface snow into pockets of wind slab at many elevations. Wind slabs may be gaining strength, but triggering is still possible in unsupported terrain.

Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 27th, 2013 2:00PM