Avalanche Forecast

Issued: Dec 8th, 2013 7:52AM

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

rbuhler, Avalanche Canada

South Columbia.

Summary

Confidence

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

Weather Forecast

The arctic ridge of high pressure will remain until Wednesday but is beginning to weaken. A series of weak frontal waves will move into northern BC and will be pushed into the southern interior by the arctic ridge. This will result in light, intermittent snowfall for the next few days. A major change in the weather is expected late Wednesday or Thursday when the arctic ridge breaks down and allows a low pressure system to enter southern BC with a westerly flow.Monday: Mostly cloudy, light snow flurries, treeline temperatures around -20C, moderate NW alpine windsTuesday: A mix of sun and cloud, light snow flurries, treeline temperatures around -15C, moderate NW alpine windsWednesday: Mostly cloudy, light snow flurries, treeline temperatures around -10C, winds switching to SW

Avalanche Summary

No natural avalanches reported since Thursday. Two ski cut avalanches reported on Saturday around Revelstoke. One size 1.5 storm slab on a NE aspect and one size 1 wind slab on a SW aspect at treeline.

Snowpack Summary

Snowpack depths are typically 100-140 cm at treeline elevation. The old storm snow (~30-60cm) overlies the late-November interface which typically consists of sun crusts on steep south facing slopes and surface hoar in sheltered areas. Some buried surface hoar has been reported on south aspect slopes near Revelstoke. These weak layers are expected to be persistent, although in many areas the upper slab is not yet stiff enough for slab avalanches. When temperatures rise, and we get additional snow, expect this interface to become a more dangerous problem. Strong NE winds after the storm caused reverse loading and wind slab formation on SE through W aspects in wind exposed areas. Lower snowpack layers include a surface hoar layer roughly 60cm above the ground and an early season rain crust at the base of the snowpack. While these layers have recently become inactive, residual risk of large, destructive avalanches exists, especially in areas with a thinner snowpack. The October crust can be found in the alpine on north aspects and the early November surface hoar appears to be isolated and drainage specific.

Problems

Wind Slabs

Northerly outflow winds have reverse-loaded and cross-loaded exposed slopes forming wind slabs below ridge crests and behind terrain features. Don't let wind slabs in unusual places catch you by surprise.

Avoid travelling in areas that have been reverse loaded by winds.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

Managing these persistent slabs can be tricky; they are stubborn and direct evidence of unstable snow may be lacking, but they can produce very destructive avalanches. Treat large open slopes with suspicion until stability is confirmed.

Dig down to find and test weak layers before committing to a line.>Caution around convexities or large, unsupported slopes>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Dec 9th, 2013 2:00PM