Avalanche Forecast

Issued: Dec 21st, 2013 10:12AM

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

swerner, Avalanche Canada

South Columbia.

The snowpack structure is complex and varies throughout the region. A conservative approach is essential.

Summary

Confidence

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

Weather Forecast

The Interior will see generally dry, cool conditions under the current NW flow. A Pacific frontal system will arrive overnight, bringing light- moderate amounts of precipitation and warmer temperatures.Sunday: Cloudy with snow amounts 10-15 cm. Alpine temperatures near -6. Light SW winds. Freezing levels near 1000 m. Monday: Snow amounts 15-25 cm. Alpine temperatures near -5. Moderate westerly ridgetop winds. Freezing levels 1300 m.Tuesday: Cloudy with sunny periods. Alpine temperatures near -7. Ridgetop winds light from the West. Freezing levels near 800 m.

Avalanche Summary

Several natural and rider triggered slab avalanches and loose-snow avalanches up to size 2 were reported on Friday.

Snowpack Summary

Average snowpack depths at treeline range from 100 cm -150 cm. New snow up to 15 cm has buried older wind slabs in exposed terrain at treeline and above. The new storm slab is touchy to rider triggers, and natural loose dry sluffing from steeper terrain exists. Buried down 40-60 cm is a surface hoar, and facet layer. This layer has recently been reactive to riders and natural triggers and both cracking and whumpfing have been noted.Digging deeper down 70-90 cm, is the late-November interface, which consists of a sun crust/ facet combo on steep south facing slopes and larger, proud surface hoar crystals in sheltered areas. This layer is generally considered to be "stubborn" to trigger. However, professionals are keeping a close eye on this layer especially with forecast new load.At the base of the snowpack the October crust is most predominant on north-facing alpine slopes with smooth ground cover. Triggering this weakness is unlikely, but if triggered the resulting avalanche would be very large and consequential.

Problems

Storm Slabs

New storm snow may be touchy to rider triggers, especially in wind effected areas. Further loading and smaller avalanches may trigger buried weak layers and create large- very large avalanches.

Avoid freshly wind loaded features.>Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.>Watch your sluff and don't get pushed into a terrain trap.>

Aspects: All aspects.

Elevations: All elevations.

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 40-70 cm of storm snow and may be susceptible to triggering by light load like skiers or riders.

Choose conservative lines and watch for clues of instability.>Dig down to find and test weak layers before committing to a line.>Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

3 - 5

Valid until: Dec 22nd, 2013 2:00PM