Avalanche Forecast

Issued: Dec 11th, 2014 7:49AM

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

Peter, Avalanche Canada

South Columbia.

Although the trend shows improvement remember that the potential for triggering an avalanche is greatest at higher elevations due to recent heavy snowfall and strong winds.

Summary

Confidence

Fair

Weather Forecast

One last system is expected to cross the province tonight bringing moderate precipitation and strong winds while maintaining high freezing levels. We could see 10-15 cm by midday Friday. Freezing levels on Friday should start near 2000 m but should drop to 1500 m late in the day. Winds are strong from the Southwest easing to light from the Northwest. The weekend looks much drier with a mix of sun and cloud. Freezing levels around 1000 m on Saturday and 500-700 m on Sunday. Winds remain light.

Avalanche Summary

Widespread natural avalanche activity up to size 3 was reported on Tuesday and Wednesday. These were primarily storm slabs in wind loaded areas. The bed surface may have been the Dec 5 surface hoar layer and/or the late-November rain crust. Slab depths are typically 30-60 cm but one report has a slab depth up to 150cm, likely in a heavily wind loaded area. Loose wet slides were also reported in lower elevation terrain.

Snowpack Summary

There are recent reports of wet snow up to 2000m elevation and moist snow to around 2400m. Higher elevations could have received 30-50 cm of dense storm snow. Strong winds are loading leeward features in the alpine. Below the new storm snow may be a layer of surface hoar which was buried on Dec 5. Below around 1800m elevation and down around 40-50cm is a rain crust but it appears that the snow above it is generally well bonded. About 1m down, a weak layer of surface hoar and/or facets can be found in some locations. A thick rain crust with facets from early November is buried over 1 m down. Snowpack tests on these deep weak layers are showing slowly improving results, but in some locations these layers are still reactive and have the potential to release large slab avalanches. We may see these deep weak layers become a problem again as the storm continues to add new load.

Problems

Storm Slabs

Storm and wind slabs continue to build, particularly above 1800-2000 m. Very strong winds may have formed wind slabs lower on the slope or cross-loaded gullies and other terrain features.

Use ridges or ribs to avoid freshly wind loaded features.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

The likelihood of triggering a persistent slab should decrease heading into the weekend but be very wary of any slope that did not release or may have been reloaded during the latest storm cycle.

Avoid common trigger zones including thin snowpack areas, near rocky outcrops, and steep alpine slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Loose Wet

This problem should become much less likely as precipitation eases off and temperatures cool later on Friday.

Be cautious of sluffing in steep terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Dec 12th, 2014 2:00PM