Avalanche Forecast

Issued: Feb 6th, 2013 9:24AM

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.

Summary

Confidence

Good

Weather Forecast

Thursday: A weak upper trough moves through the region bringing unsettled conditions and light snow accumulations of 5 cm. Ridgetop winds will light and blowing from the West. Treeline temperatures near -4 and freezing levels will be around 1100 m. Friday: Ridge of high pressure moves in with residual moisture and cloudy cover bringing only trace snow amounts. Ridgetop winds will switch and blow light from the NW. Treeline temperatures near -6 and freezing levels will be in the valley bottom.Saturday: Ridging continues accompanied by a fast moving, short lived weak disturbance. Trace of snow expected with ridgetop winds blowing moderate from the NW. Treeline temperature near -8 and freezing levels remain in the valley.

Avalanche Summary

Natural loose snow sluffing from steep 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 hoar surface 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. Areas of concern are in the immediate lees of slopes and behind terrain features like ridgelines and ribs.

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

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 7th, 2013 2:00PM