Avalanche Forecast

Issued: Feb 7th, 2013 9:55AM

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.

swerner, Avalanche Canada

Purcells.

Weak layers within the upper snowpack have yet to be tested by the effects of the sun. Blue skies and fresh snow may tempt you into steeper and bigger terrain. Maintain a diligent approach to terrain selection to best manage the current conditions.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

Friday: A weakening upper trough moves out of the region as a ridge of high pressure makes its way in. The initial changes in the weather pattern will bring only trace amounts of new snow and broken cloud. Periods of sunshine and solar radiation may exist. Ridgetop winds will be light-moderate from the NW. Treeline temperatures will be near -5 and freezing levels at valley bottom. Saturday: The ridge of high pressure builds and brings dry conditions with periods of scattered to few clouds allowing some sunny alpine skies. Ridgetop winds will blow light-moderate from the NW. Treeline temperatures near -3 and freezing levels rising to 1300 m then dropping back to valley bottom overnight.Sunday: The upper ridge strengthens with continued dryer conditions. Ridgetop winds light from the NW. Treeline temperatures near -6 and freezing levels around 1000 m.

Avalanche Summary

Several small slab avalanches occurred size 1 from steep, cross-loaded terrain features. A skier triggered size 1.5 slab avalanche occurred from a NE aspect at 2300 m. Natural loose dry sluffing continued from steep unsupported terrain.

Snowpack Summary

Wind slabs exist in the alpine and at treeline on lee slopes and behind ridgelines. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm. However, areas that have buried surface hoar seem to be most touchy. Continued freezing temperatures overnight have helped to strengthen the moist surface layers that developed during warm period last weekend.The mid-pack is generally well settled. The average snowpack depth at treeline elevations is near 130 cm.

Problems

Wind Slabs

New wind slabs continue to be reactive to light additional loads like skiers and sledders. Areas of concern are in the immediate lees of slopes and behind terrain features like ridgelines and ribs. Cornices have grown and may threaten slopes below.

Avoid lee and cross-loaded terrain near ridge crests.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

The recent storm snow continues to settle into a cohesive slab above weak layers and variable old surfaces that comprise of buried wind slabs, surface hoar, and crusts. These weak layers exist 30-50 cm below the surface.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Feb 8th, 2013 2:00PM