Avalanche Forecast

Issued: Jan 4th, 2012 9:24AM

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

swerner, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Thursday

Weather Forecast

As the cold front sweeps through the interior Wednesday afternoon we'll see cooling temperatures and moderate precipitation amounts. Wednesday Night: Snow amounts up to 15cms. Ridgetop winds 40-50km/hr from the SW. Alpine temperatures near -4. Freezing levels down to 700m. Thursday: Snow amounts up to 10cms in the Western parts of the region, with up to 5cms in the East. Freezing levels around 700m. Ridgetop winds 40-50km/hr from the SW, switching to 30km/hr from the NW. Friday/Saturday: Snow amounts near 5cms. A ridge of high pressure builds bringing cooling, and dryer conditions into Saturday.

Avalanche Summary

Reports from the Eastern part of the region saw numerous natural avalanches up to size 2.5 , on North aspects @2000m. Many of the recent avalanches have occurred due to large triggers (cornice fall, explosive testing). On Monday there was a size 2 sled triggered avalanche that occurred west of Revelstoke on a South aspect near 1800m. No injuries reported. The mid-December persistent weak layer is buried down 80-120cms and is still a layer of concern. Avalanches that are failing on this layer are large-very large (sz 2-3.5). As the natural activity has somewhat tapered off, the sensitivity to skier, or sledder triggers are likely. Remote triggering (setting off avalanches from afar, with wide fractures) continues to be reported. I would also be suspicious of low angle terrain in the trees. It seems to be catching people by surprise.

Snowpack Summary

New snow up to 10cms has fallen over the region. This blankets all elevations and buries a new surface hoar layer that formed over the New Year. Reports indicate that the SH crystals range in size up to 10mm. The previous storm snow that fell over Christmas has been blown around by steady SW winds and has formed wind slabs. Wind slabs are widespread and found in exposed alpine and treeline locations. Below the surface 80-120cms lurks a surface hoar/facet/crust interface (persistent weak layer) from mid-December. Testing on this layer has shown moderate to hard results with sudden planer characteristics. This weak layer has been very reactive; producing large, destructive avalanches. It still remains a layer of concern and should continue to be on your radar. Below this layer sits a strong mid pack.

Problems

Wind Slabs

In the alpine and at treeline SW winds will redistribute storm snow into wind slabs on lee slopes. I'd be suspect of any open, wind exposed locations. Once moving, a wind slab could step down and trigger a large avalanche.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

A cohesive slab sits over a touchy surface hoar weakness buried in mid-December. This layer is still touchy and susceptible to rider triggers. Avalanches on this layer will be large, destructive and may fracture across surprisingly far distances.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

3 - 7

Cornices

With rising alpine temperatures cornices may become weak. The load could trigger the slope below and step down to the mid-December surface hoar layer.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 6

Valid until: Jan 5th, 2012 8:00AM