Avalanche Forecast

Issued: Feb 7th, 2013 9:47AM

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.

Weak layers within the upper snowpack have yet to be tested by the effects of the sun. Blue skies and fresh snow may tempt you into steeper and bigger terrain. Maintain a diligent approach to terrain selection to best manage the current conditions.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Friday: A weakening upper trough moves out of the region as a ridge of high pressure makes its way in. The initial changes in the weather pattern will bring only trace amounts of new snow and mostly cloudy skies. By the afternoon broken cloud cover may exist, especially in the Eastern ranges of the region allowing some sunshine. Ridgetop winds will be light from the North. Treeline temperatures will be near -5 and freezing levels around 700 m. Saturday: The ridge of high pressure builds and brings dry conditions with scattered to few clouds allowing sunny alpine skies. Ridgetop winds will blow light-moderate from the NW. Treeline temperatures near -3 and freezing levels rising to 1000 m. Sunday: The upper ridge strengthens with continued dryer conditions. Ridgetop winds light from the NW. Treeline temperatures near -5 and freezing levels around 900 m.

Avalanche Summary

Natural avalanche activity continues with slab avalanches up to size 2.5. Most aspects and elevations above 1400 m are the main performers. Rider triggered avalanches up to size 2 continue to be triggered on the early February interface and the January 26th interface. The persistent slab is touchy and reactive to light loads like skiers and snowmobilers. Heads up out there! Suspect avalanche activity to continue through the forecast period, additional concerns being solar radiation as a natural trigger.Â

Snowpack Summary

New snow (20-40 cm) adds to the persistent slab problem which sits on a surface hoar layer and a sun crust layer that developed at the beginning of February and is reactive. An even thicker slab continues to be reactive especially on solar aspects where an old sun crust has been buried and at treeline and below on steep convex slopes that host well preserved surface hoar at the January 23rd interface (between 40-80 cms down). Wind slabs persist in the alpine and at treeline. The loading pattern may change due to winds switching from the SouthWest to the NorthWest and form pockets of wind slab in unsuspecting places. At lower elevations a melt-freeze crust has formed due to the recent high freezing levels.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, however this interface has been less reactive.

Problems

Persistent Slabs

Persistent slabs are 40-80 cm thick and continue to be reactive above variable sliding surfaces comprising of surface hoar, crusts and facets. They are easily triggered by the weight of a skier or a machine.

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 committing to a line.>Good group management is essential to manage current conditions safely.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 5

Wind Slabs

Rider triggers are possible. Lee slopes and behind terrain features like ribs and ridges are a concern. Changing winds may load unsuspecting aspects. In sheltered areas watch for natural loose sluffing over convex rolls and from steep terrain.

Avoid freshly wind loaded features.>Use ridges or ribs to avoid pockets of wind loaded snow.>Assess slopes carefully and use safe travel techniques.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Valid until: Feb 8th, 2013 2:00PM