Avalanche Forecast

Issued: Mar 2nd, 2013 9:56AM

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

ghelgeson, Avalanche Canada

South Columbia.

The storm may be over, but the mountains are currently primed for skier/sledder triggered avalanches.

Summary

Confidence

Fair

Weather Forecast

Synopsis: The region should see one last burst of precip as the moisture laden system moves off to the east Saturday night. Sunday/Monday bring a drying trend that should persist through Monday evening. Saturday Night: 10/15 cm/mm snow/rain. Freezing level around 1500 at Sunset, steadily lowering through the night. Moderate to Strong SW winds.Sunday: Freezing level starts at 500m rising to 900m during the day. No precipitation expected. Cloudy skies. Winds switch to the NE, light at treeline, strong at ridge top. Monday: Freezing level at valley bottom. No precip. Clear skies. Winds light and variable.Tuesday: Freezing level at valley bottom, rising to 1000m during the day. Precip begins around lunch time as another deep upper low approaches the region.

Avalanche Summary

A widespread natural avalanche cycle occurred on Friday with many reports of avalanches running up to size 4 on all aspects and elevations. Remember that we define a size 4 as being large enough to destroy a railway car or semi truck. The observations are humbling to say the least.

Snowpack Summary

A heavy dump of moist new snow has added to recent storm totals (now 120-150 cm over a two-week period). The snow surface became wet as snow gradually turned to rain to approximately at 1900 m. I expect a crust to develop at lower elevations as temperatures drop Saturday night. Below the storm snow lies a highly reactive weak layer of surface hoar (and/or a crust) which was buried on February 12th. Strong southwest winds have redistributed the new snow into deep wind slabs on exposed lee slopes and cross-loaded gully features. The February 12 layer is primed for triggering and has been reacting readily to both natural and human triggers on all aspects and a wide range of elevations. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. In particular, in the Monashees, a rain crust buried down 150 cm has been responsible for a couple of recent large, surprising avalanches. Immediately following the current storm, the presence of this deeper weak layer could further increase the potential size of avalanche events.

Problems

Storm Slabs

Natural activity should taper off Sunday, but conditions remain primed for human triggering due to to the presence of a deeply buried weak layer.

Avoid exposure to overhead avalanche terrain, as large avalanches may reach the end of runout zones.>Avoid paths that have not avalanched recently.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 7

Persistent Slabs

A weak layer of surface hoar and/or a crust is now down 100 cm or more. This weakness has been susceptible to remote triggering and has been reported from all elevations and aspects.

Avoid runouts where triggering slopes from below is possible.>Remote triggering is a concern, watch out for adjacent slopes and do not expose yourself to overhead hazard.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

3 - 8

Cornices

The storm has left many large cornices in it's wake on lee slopes, many of which are teetering on the brink of failure. Cornice fall has the potential to initiate large destructive avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Mar 3rd, 2013 2:00PM