Avalanche Forecast

Issued: Dec 5th, 2012 9:13AM

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

triley, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Overnight and Thursday: Cloudy with some convective flurries in the west areas of the region. Mostly cloudy on Thursday. Some light precipitation during the day bringing 3-5 cms to higher elevations. Light westerly winds are expected.Friday: Mostly cloudy with cooler temperatures in the alpine and freezing levels down to the valleys. Some light convective flurries in the morning.Saturday: Cloudy with valley fog in the morning. Some sunny periods in the afternoon.

Avalanche Summary

Some small stiff wind slab releases were reported from explosive control during the storm on Tuesday. There is one report of a size 3.0 avalanche from very steep un-skiable terrain on a lee aspect in the northeast of the region in the Selkirks. There is also a report from the north of the region in the Monashees of a size 3.0 avalanche on a 30-40 degree slope NE aspect at 2200 metres that was 100-150 cms deep and ran on the early november rain crust.

Snowpack Summary

Very strong winds and warm temperatures on Tuesday created some stiff wind slabs in the alpine and open areas at treeline. The Selkirks and Eastern Monashees total snowpack depth has reached as much as 270cm at treeline. 3-10mm surface hoar buried late last week can be found down 50-80cm and has been reactive to light triggers on unsupported features at treeline elevations. The well-settled and strong mid-pack may be bridging deeper weaknesses; however, recent snowpack tests produced occasional hard but sudden results on the early November facet/crust combination down 100-190cm in treeline and alpine areas. Furthermore, favorable slab structure for step-down fractures can contribute to the persistence of this deep weakness. Meanwhile in the Okanagan, relatively warm temperatures are promoting a well consolidated 70-80cm treeline snowpack with isolated small thin wind slabs.

Problems

Wind Slabs

Fresh wind slabs can be found well below ridge crests, behind terrain features and in cross-loaded gullies in any wind-exposed terrain. Expect these deep drifts to be very touchy.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

2 - 5

Persistent Slabs

A variable surface hoar layer may be found buried down 50-80 cms. This layer was buried in most parts of the region on Nov.28th. This may be found mostly at treeline between 1700-2100 metres.

Be aware of thin areas that may propagate to deeper instabilites.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 6

Deep Persistent Slabs

An old facet/crust combination deep in the snowpack may wake up with heavy triggers, smaller avalanches stepping down, or triggering from thin-spots. Although unlikely, deep persistent slab avalanches can be massive.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Dec 6th, 2012 2:00PM