Avalanche Forecast

Issued: Feb 6th, 2013 9:32AM

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

swerner, Avalanche Canada

South Columbia.

Summary

Confidence

Good

Weather Forecast

Thursday: A weak upper trough moves through the region bringing unsettled conditions and light snow accumulations 5-10 cm. Ridgetop winds will light and blowing from the West. Treeline temperatures near -3 and freezing levels around 700 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 North. Freezing levels stationary around 700 m.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 -4 and freezing levels around 900 m falling to valley bottom overnight.

Avalanche Summary

Natural avalanche activity continues with loose dry and slab avalanches up to size 2. North through NorthEast aspects producing the slab activity, and South generally producing the loose dry avalanches and sluffing from steep terrain features. Rider triggered avalanches up to size 2 continue to be triggered on the early February interface and the January 26th interface that is buried 40-80 cm below the surface. One skier triggered slab avalanche size 2.5 was initiated from a North aspect at 2100 m, failing on the Feb. interface.

Snowpack Summary

Wind slabs continue to develop in the alpine and at treeline on lee slopes and behind terrain features. Below the surface a couple persistent weak layers exist. Most recently, 20-40 cm of new snow buries a surface hoar layer and a sun crust layer that developed at the beginning of February. Lower down (40-80 cm) sits the January 23rd interface also comprising of surface hoar, and crusts. These layers continue to be reactive especially on steep solar aspects, treeline and below treeline over steep convex rolls or sheltered slopes where surface hoar would most likely to form. The mid-pack is well settled and strong. At lower elevations a melt-freeze crust has formed due to the high freezing levels from last weekend.

Problems

Persistent Slabs

Persistent slabs continue to be reactive above variable sliding surfaces comprising of surface hoar, crusts and facets that are buried 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 before dropping into your line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Wind Slabs

In exposed areas wind slabs could be rider triggered. Lee slopes and behind terrain features like ribs and ridges are a concern. In sheltered areas watch for natural loose sluffing over convex rolls and from steep terrain.

Avoid freshly wind loaded features.>Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Valid until: Feb 7th, 2013 2:00PM