Avalanche Forecast

Issued: Feb 4th, 2013 9:22AM

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

South Columbia.

If your receive less then 20 cm of snow in your local riding area, consider the danger ratings to be a step to high on Tuesday.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Tuesday: The trailing cold front has brought temperatures back down to seasonal norms. The next well developed system brings light-moderate snow amounts with localized heavy amounts to some SW facing slopes. Ridgetop winds will blow strong from the West and alpine temperatures will be near -8. Freezing levels will hover around 1200 m. Wednesday: Upper disturbances embedded in the SW flow will bring continued stormy conditions. Snow amounts 10-20 cm throughout the day, tapering off overnight. Ridgetop winds will continue to 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 South. Alpine temperatures near -9 and freezing levels will stay near 1000 m in the afternoon then falling overnight.

Avalanche Summary

Wind slabs also continued to release naturally or were triggered by skiers up to size 2. Region wide, numerous reports of skier triggered slab avalanches up to size 2 were initiated. Most of these avalanches have failed on the January 23 persistent weak layers. These occurred anywhere from 1600 m-2200Â m and on a variety of aspects. With forecast storm snow and wind transport these layers may become more reactive naturally under the new loads.

Snowpack Summary

Wind slabs continue to develop in the alpine and at treeline. Forecast storm snow will blanket a sun crust that has developed on steep Southerly aspects, and a melt-freeze crust has developed at lower elevations due to the recent high freezing levels. The recent storm slab continues to be reactive on solar aspects where an old sun crust has been buried andÂ at treeline and below on steep convex slopes that host preserved buried surface hoar at the January 23rd interface (between 40-80 cms down). The mid-pack is well settled and strong. There are a few locations that continue to find a well preserved surface hoar layer from early January that is buried down about 90-100 cms and has been less reactive.

Problems

Wind Slabs

Old wind slabs are expected to continue to be triggered by light additional loads. New wind slabs are expected to build during the next pulse of precipitation.

Avoid freshly wind loaded features.>Use ridges or ribs to avoid pockets of wind loaded snow.>Highmark or enter your line well below ridge crests to avoid wind loaded pillows and use representative small slopes as indicator slopes before committing to anything bigger. >

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

Forecast snow and strong winds will put an additional load on weak layers. They continue to be reactive above variable sliding surfaces that are down 40-80 cm below the surface.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Whumpfing is direct evidence of a buried instability.>Dig down to find and test weak layers from a safe location before dropping into your line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Valid until: Feb 5th, 2013 2:00PM