Avalanche Forecast

Issued: Jan 31st, 2013 9:20AM

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.

Avalanche Canada swerner, Avalanche Canada

Summary

Confidence

Good

Weather Forecast

The offshore upper ridge will start to move onto the province pushing the polar front to the North bringing rising freezing levels, and sunny skies Friday afternoon into Saturday. Friday: A mild SW flow will show no new precipitation and ridgetop winds will be light from the West. Alpine temperatures will rise to 3.0 degrees and freezing levels will rise to 2200 m.Saturday: Continued warm temperatures and sunny skies. Alpine temperatures will rise to 4.0 degrees and freezing levels will be near 2100 m. Ridgetop winds will be light from the SW.Sunday: Dominating ridge will start breaking down bringing light-moderate precipitation. Alpine temperatures will drop to -4.0 with freezing levels falling to 1200 m.

Avalanche Summary

From the Northern parts of the region, a natural slab avalanche size 2.5 was reported from a East aspect at 2000 m, failing on the buried surface hoar layer from early January. This layer has been fairly quiet recently, goes to show it may still be reactive in isolated areas. Another noted size 2.0 slab avalanche failed on the recent buried weakness from a NNW aspect around 1600 m.Several rider triggered slab avalanches up to size 2.0 have been reported south of the Coquihalla. These avalanches were triggered from SE-E aspects  at 1600-1700 m, failing on the most recently buried crust/surface hoar/facet layer.

Snowpack Summary

Up to 30 cm of snow fell over the past few days with light to moderate winds. This snow seems to be settling and gaining strength although forecast rising alpine temperatures and sunny skies will affect and weaken the upper snowpack. Wind slabs are possible behind ridges and ribs and may be touchy to rider triggers. Wind slabs could also be found in unsuspecting places due to changing winds from NW-SW. Be cautious of cross-loaded terrain features. The new snow has buried a variety of surfaces including old wind slabs, crusts and large surface hoar crystals which can be found in sheltered terrain below treeline. The most recent buried crust/surface hoar down approx. 10-30 cm are producing moderate-sudden planar and resistant test results, and should remain a layer to watch. Down deeper sits another surface hoar layer (40-80 cm) which seems to be gaining strength.Near the base of the snowpack, a crust/facet layer exists, which is now unlikely to be triggered, except perhaps by heavy triggers in unsupported, shallow, rocky terrain where more faceting has taken place.

Problems

Wind Slabs

An icon showing Wind Slabs
New snow has been blown behind ridges and ribs with switching winds and may be rider triggered. This is a less typical pattern so east and south facing slopes as well as cross-loaded features are more suspect. Cornices may become weak with warming.
Avoid freshly wind loaded features.>Use extra caution on lee and cross-loaded terrain near ridge crests.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Loose Wet

An icon showing Loose Wet
Warming and the effects of solar radiation will likely weaken the upper snowpack and produce loose wet avalanches. Natural avalanches and snowballing are obvious indicators of the snowpack deteriorating.
Avoid slopes during warming and high solar radiation, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

An icon showing Persistent Slabs
Buried down 30-60 cm exists a surface hoar/crust/facet layer. This layer of concern seems to be most reactive in sheltered locations over convex rolls and steeper terrain features.
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

Unlikely - Possible

Expected Size

2 - 5

Valid until: Feb 1st, 2013 2:00PM