Avalanche Forecast

Issued: Dec 19th, 2013 7:47AM

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

Peter, Avalanche Canada

South Columbia.

Summary

Confidence

Fair

Weather Forecast

Friday: Cloudy with light to moderate snowfall 5-15 cm. The freezing level is at valley bottom and ridgetop winds are light to moderate from the west-northwest. Saturday: Mainly cloudy with a chance of flurries. The freezing level could jump to 700 m and moderate gusty west-northwest winds continue. Sunday: Possible sunny breaks and flurries. The freezing level could climb to 1000 m and the upper flow continues to be northwesterly.

Avalanche Summary

Several natural and rider triggered loose-snow avalanches (sluffs) and small wind slabs were reported on Wednesday. There was also a report of a size 3 natural slab avalanche from a southwest-facing alpine slope that ran full path.

Snowpack Summary

5-10 cm of dry new snow covers the previous storm snow and wind slabs in higher exposed terrain. Dense wind slabs are most likely on exposed north through southeast facing slopes. A weak layer of surface hoar, facetted snow, and/or a crust is now down around 40 cm in the south and up to 60 cm further north. This layer has recently been reactive to riders and natural triggers and both cracking and whumpfing have been noted. The late-November interface, which consists of a sun crust on steep south facing slopes and surface hoar in sheltered areas, is buried 60-90cm below the surface and is generally considered to be "stubborn" to trigger. At the base of the snowpack the October crust is lurking in specific terrain, like north-facing alpine slopes with smooth ground cover. Triggering this weakness is unlikely, but if triggered the resulting avalanche would be very large and dangerous.

Problems

Wind Slabs

Recent strong westerly winds have created fresh wind slabs in exposed lee terrain and cross-loaded features. Rider triggering remains possible, particularly in steep unsupported terrain.

Use ridges or ribs to avoid pockets of wind loaded snow.>Avoid avalanche terrain during periods of heavy loading from new snow and wind.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

A buried persistent weak layer of facets, surface hoar, and/or a crust is buried by 40-60 cm of storm snow and may be susceptible to triggering by light load like skiers or riders.

Choose well supported terrain without convexities.>Choose conservative lines and watch for clues of instability.>Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Dec 20th, 2013 2:00PM