Avalanche Forecast

Issued: Feb 5th, 2013 9:15AM

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.

Summary

Confidence

Fair - Due to variable snowpack conditions

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 10-15 cm. Treeline temperatures steady -4 and freezing levels 1100 m falling to 700 m overnight.Thursday: Unsettled conditions continue, bringing light snow accumulations. Ridgetop winds will switch and blow from the SW. Treeline temperatures near -3 and freezing levels rising to 1200 m in the afternoon, falling to valley bottom overnight.Friday: Outlook shows surface and upper ridge building, bringing dryer conditions and valley cloud. Treeline temperatures near -7 and freezing levels hovering around 800 m. Ridgetop winds blowing moderate from the NW.

Avalanche Summary

Natural avalanche activity continues up to size 2, with a glide crack release size 2.5. Natural activity has occurred on most aspects, with sluffing from steep terrain features. Rider triggered avalanches up to size 2 continue to be triggered on the January 26th interface that is buried 40-80 cm below the surface at treeline and below treeline elevations. 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. New snow sits on a surface hoar layer that developed at the beginning of February (20-40 cm down) and a sun crust that has developed on steep Southerly aspects. At lower elevations a melt-freeze crust has formed 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

In exposed areas wind slabs will likely continue to be triggered by light loads. 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 and use safe, small representative slopes as indicator slopes before committing to anything bigger.>Avoid traveling on or near terrain traps where sluffing may have severe consequences.>

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.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

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