Avalanche Forecast

Issued: Feb 4th, 2013 9:02AM

The alpine rating is considerable, the treeline rating is moderate, 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 on Tuesday

Weather Forecast

Tuesday: The trailing cold front has brought temperatures back down to seasonal norms. The next well developed system brings snow amounts near 10 cm. Ridgetop winds will blow strong from the SW and alpine temperatures will be near -7. Freezing levels will hover around 1400 m. Wednesday: Upper disturbances embedded in the SW flow will bring continued stormy conditions. Snow amounts 10-15 cm throughout the day, tapering off overnight. Ridgetop winds will be strong from the West. Alpine temperatures near -9 and freezing levels around 1100 m. Thursday: Weak unsettled conditions will prevail with no significant precipitation. Ridgetop winds will blow light from the SW. Alpine temperatures will be near -9 and freezing levels will hover at 1000 m in the afternoon, then falling overnight.

Avalanche Summary

No new natural avalanche activity has been reported. An explosives control mission triggered a slab avalanche size 2.5 on a SE aspect around 2500 m.

Snowpack Summary

Forecast strong SW winds and new snow will continue to build wind slabs in the alpine and at treeline. 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 touchy. Continued freezing temperatures overnight have helped to strengthen the moist surface layers that developed during the weekend warm period. Rising freezing levels forecast during the next pulse of moisture may weaken the old storm slab at lower elevations. The mid-pack is well settled and there are no reported deep layers of concern.

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 freshly wind loaded features.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

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 5th, 2013 2:00PM