Avalanche Forecast

Issued: Jan 3rd, 2012 9:21AM

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

Good - -1

Weather Forecast

A small "Pineapple" (or maybe we should refer to it as a Papaya due to lack of moisture in the Interior) is pushing through the Southern ranges. Tuesday night snow amounts up to 10cms. Wind 60-90km/hr from the SW. Light precipitation during the day. Freezing levels rising to 2000m through the day. Wednesday night snow amounts 10-20cms with 20cms more realistic in the Northern parts of the region, less in the South. Freezing levels fall to 1000m. Thursday: Snow amounts near 10cms. Freezing levels falling from 1000m to valley bottom by Thursday afternoon. Friday: to 600m by early afternoon. Friday: Mix of sun and cloud. Light snow amounts. Light winds from the SE. Freezing levels valley bottom.

Avalanche Summary

In the Selkirks continued avalanche activity is being reported. Many of the recent avalanches have occurred due to large triggers (cornice fall, explosive testing). Yesterday 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, even below treeline. 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 - 5

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, stepping down to the mid-December surface hoar layer.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 6

Valid until: Jan 4th, 2012 8:00AM