Avalanche Forecast

Issued: Feb 5th, 2013 9:18AM

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

swerner, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Wednesday: Today the region sits under a weakening zonal flow maintaining moderate-strong ridgetop winds from the West. An upper disturbance embedded in the flow will bring snow amounts 5-10 cm. Treeline temperatures steady -4 and freezing levels steady around 1100 m. Thursday: Unsettled conditions continue, bringing light snow accumulations. Ridgetop winds will switch and blow from the SW. Treeline temperatures near -3 and freezing levels hovering around 1300 m, falling to valley bottom overnight.Friday: Outlook shows surface and upper ridge building, bringing dryer conditions and valley cloud. Treeline temperatures near -4 with freezing levels hovering around 1100 m. Ridgetop winds blowing moderate from the NW.

Avalanche Summary

Skier triggered size 1 slab avalanches were reported. These were initiated in the immediate lee of slopes primarily on NE aspects around 2200 m. No new natural activity has been reported.

Snowpack Summary

Forecast strong westerly winds and new snow will continue to build wind slabs in the alpine and at treeline on lee slopes and behind ridgelines. The recent storm slab continues to be reactive down 30-50 cms at treeline and below. This slab sits on a variety of old interfaces, 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 the weekend warm period. The mid-pack is generally well settled. The average snowpack depth at treeline elevations is near 130 cm.

Problems

Wind Slabs

Old wind slabs continue to be reactive to light additional loads. Expect new wind slabs to develop with the next pulse of moisture. Areas of concern are lee slopes and behind terrain features like ridgelines and ribs.

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 and use small representative slopes as indicator slopes before committing to anything bigger.>

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.

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 dropping into your line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 5

Valid until: Feb 6th, 2013 2:00PM