Avalanche Forecast

Issued: Dec 27th, 2013 7:53AM

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 Deep Persistent Slabs.

Peter, Avalanche Canada

Cariboos.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Saturday: Mainly cloudy with a chance of flurries and possible sunny breaks. The freezing level drops to valley bottom and winds are light to moderate from the northwest. Sunday: Mainly cloudy with a chance of flurries or light snow – around 5 cm. The freezing level is near valley bottom and winds are moderate gusting strong from the W-NW. Monday: Flurries or periods of snow. The freezing level should remain at valley bottom.

Avalanche Summary

Reports from the past couple days are very limited. It's likely that the combination of new snow, wind, and mild temperatures kicked off a natural avalanche cycle in some areas over the past couple days. The additional load may have also been enough to trigger deep persistent weaknesses in isolated areas. Cooler temperatures and drier conditions on the weekend should help to stabilize the snowpack, but rider triggering will certainly remain a concern. Watch for steep slopes that did not previously avalanche, wind loaded areas, and high north-facing terrain with variable snow cover.

Snowpack Summary

An additional 20-30 cm of snow has fallen accompanied by moderate to strong W-SW winds and mild temperatures. New dense wind slabs are likely in exposed lee terrain at and above treeline. Up to 80cm of snow now sits on a variety of weaknesses from early December (surface hoar, faceted snow, and/or a crust). An older layer of surface hoar or facets from late November can be found deeper in the snowpack. Recent snowpack tests results vary but some are showing this layer "pop" with medium loads, indicating a potential for human triggering.Snowpack depths vary, but in general up to 150 cm of snow can be found at treeline, with 100-200 cm in the alpine. In many places we're still dealing with a relatively thin snowpack (thanks to a windy early season) so there's not a whole lot of snow between riders and the sugary snow (facets) near the ground. The basal facet/crust combo has been recently active in parts of the region.

Problems

Storm Slabs

The new snow make take a couple days to settle and stabilize. Watch for fresh new wind slabs in exposed north and east facing terrain at higher elevations.

Use caution in lee areas in the alpine. Recent wind loading have created wind slabs.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

Several persistent weaknesses exist in the upper and mid-snowpack and could be triggered by the weight of a skier or rider.

Be aware of the potential for large, deep avalanches.>Use conservative route selection, stick to moderate angled terrain with low consequence.>Whumpfing is direct evidence of a buried instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

Triggering the weakness near the base of the snowpack might take a large load (i.e. big cornice chunk) or triggering from a thin snowpack area. Avoid big alpine slopes that are peppered with rocks or look to have variable snow cover.

Avoid rock outcroppings, steep convexities and anywhere the snowpack feels thinner than average.>

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Dec 28th, 2013 2:00PM