Avalanche Forecast

Issued: Feb 11th, 2013 3:00PM

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

pmarshall, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Tuesday: A frontal system approaches the coast and moves across the province. Flurries are expected during the day (2-3 cm) and moderate snow in the evening and overnight (~10 cm). Winds increase to strong from the southwest later in the afternoon. The freezing level is around 1200 m. Wednesday: Possible flurries early then a mix of sun and cloud. The freezing level drops to 500 m. Winds are light from the northwest. Thursday: A mix of sun and cloud. The freezing level is near valley bottom. Winds are light from the west.

Avalanche Summary

Natural avalanche activity loose and slab avalanche activity up to size 2.5 continues through the region. Rider triggered avalanches are ongoing and we have continued to receive reports of rider triggered slab avalanches up to size 2. Most of these cases still involving the persistent weak layers below the surface. There was one report of a size 3.5 explosive triggered avalanche on Sunday. This was triggered with large explosives in very steep terrain and resulted in a crown that was around 40 cm deep and propagated at least 300 m wide.

Snowpack Summary

The snow surface consists of new wind slab in exposed alpine terrain, a sun crust on solar aspects, and surface hoar and/or facets on shady slopes. Below this 20-40 cm of settled storms snow sits on a surface hoar and sun crust layer that developed at the beginning of February. This layer continues to be reactive to rider triggers. Deeper down (between 40-80 cm) sits an old sun crust and well preserved surface hoar that was buried on January 23rd. This persistent slab has been reactive over the past few days, especially from solar aspects and at treeline and below treeline over steeper convex slopes. During recent snowpack testing this layer has shown moderate compression results with sudden planar to resistent planar characteristics. This layer is getting stronger over time and less likely to trigger, but if triggered it will still produce a significant avalanche. The mid-pack is generally well settled and strong.

Problems

Wind Slabs

Wind slabs exist on lee slopes and behind terrain features like ribs and ridges. Recent changing winds may load unsuspecting aspects and catch you by surprise.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

Persistent slabs are 40-80 cm thick and continue to be reactive above variable sliding surfaces comprising of surface hoar, crusts and facets. They may be triggered by the weight of a skier or a machine.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Feb 12th, 2013 2:00PM