Avalanche Forecast

Issued: Feb 1st, 2013 9:06AM

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

swerner, Avalanche Canada

Sea To Sky.

Rising temperatures and intense solar radiation is the driving force for the Avalanche Danger Ratings on Saturday.

Summary

Confidence

Good

Weather Forecast

Saturday: The dominating ridge of high pressure will bring significant warming and sunny skies. Alpine temperatures could get as high as plus 4.0 degrees with freezing levels rising near 2400 m and sunny skies. Ridgetop winds will be light from the SW.Sunday: The ridge will weaken, allowing the next frontal system to move in. Skies will generally be cloudy and no significant precipitation is expected. Alpine temperatures will fall to -3.0 and freezing levels will be near 1300 m. Ridgetop winds will blow moderate from the SW.Monday: Unsettled conditions with snow amounts up to 10 cm. Ridgetop winds will be light from the SW. Alpine temperatures near -4.0 and freezing levels hovering at 1300 m in the afternoon.

Avalanche Summary

No natural avalanche activity has been reported.On Thursday, numerous natural slab avalanches size 1.0-2.5 on NE-E aspects, one being a cornice release, and others releasing on older buries surface hoar layers. Rider triggered size 1.0 on SE aspect at 1500 m on most recently buried surface hoar/crust interface. With forecast rising freezing levels and a high solar influence, loose wet avalanches are likely.

Snowpack Summary

Wind slabs can be found behind ridges, ribs and on lee slopes (NW-NE).The upper snowpack is showing continued settlement and gaining strength, although above zero alpine temperatures and sunny skies will likely weaken it. Down 20-50 cm sits a persistent interface comprising of crusts, facets and surface hoar crystals. Recently, this layer has been touchy in sheltered areas at treeline and below (where the surface hoar had a chance to form). Down deeper sits another surface hoar layer (40-80 cm) which seems to be gaining strength with very little recent reactivity on it.The mid pack is generally well settled, which may be bridging a basal facet/crust layer in deeper snowpack areas. The average snowpack depth at treeline is near 180 cm.

Problems

Wind Slabs

Recent winds have formed wind slabs in unsuspecting places (reverse loaded). Wind slabs may been touchy to rider triggers. Stiff, hollow snow below your feet is a good indicator of unstable snow. Cornices may become weak and fail with warming.

Use ridges or ribs to avoid pockets of wind loaded snow.>Extra caution around wind loaded features.>Pay attention to overhead hazards like cornices.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Loose Wet

Warming and the effects of solar radiation will likely weaken the upper snowpack and produce loose wet avalanches. Natural avalanche activity, snowballing, moist or wet snow are obvious indicators of of the snowpack deteriorating.

Avoid slopes when warming and the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

Buried down 20-50 cm exists a surface hoar/crust/facet layer. This layer has been reactive in sheltered locations over convex rolls and steeper terrain features. With warming, this layer may become more reactive.

Dig down to find and test weak layers before committing to a line.>Whumpfing is direct evidence of a buried instability.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 5

Valid until: Feb 2nd, 2013 2:00PM