Avalanche Forecast

Issued: Dec 14th, 2012 8:27AM

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

istorm, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Good

Weather Forecast

Synopsis: A windy pacific storm is heading your way Saturday, clearing out Sunday.Saturday: 20 to 30 mm additional precipitation bringing storm totals in the range of 35 to 55 mm of water (somewhere around 40 to 70 cm of snow); Strong SW winds easing and veering W late in the day; freezing level below 500 m with alpine temperatures around -5Sunday & Monday: drier with less than 5 cm of snow; cooler temperatures with freezing level at the valley bottom and around -8 in the alpine; light SW wind Saturday becoming light E wind on Monday.

Avalanche Summary

In the north, only sluffing was reported recently; however, reports from a few days ago (after the previous storm) may provide insight into what might happen with this incoming storm. I'm thinking about a few big avalanches on the basal facets / rain crust / glacier ice. Smaller storm-snow slides or dropping cornice noses could be the "heavy load" that "steps down" to this weakness.

Snowpack Summary

Storm snow will continue to get deeper in the region, likely creating some short-term unstable layers but also hiding some previous wind slabs. Because the wind shifted around the clock (outflow and onshore),slabs could be on most aspects in alpine and exposed treeline slopes. Previously, spotty surface hoar was reported in the upper snowpack which may remain under this new snow in sheltered treeline areas. A key concern is a November facet/crust layer which can be found near the base of the snowpack. This layer, which is widespread, can be triggered from thin-spot trigger points, or with a heavy load, such as storm slabs stepping down, cornice fall or a sled track trenching.

Problems

Storm Slabs

Storm snow instabilities are likely on many steeper slopes. New windslabs will form behind ridges & ribs, and with strong or shifting winds may end up forming lower down the slope than might be typically expected.

Assess start zones carefully and use safe travel techniques.>Avoid areas with overhead hazard.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Deep Persistent Slabs

Deeply buried weaknesses exist, and the incoming storm could test their strength. Dropping cornices or smalller surface slides could step down.

Avoid exposure to overhead avalanche terrain, as large avalanches may reach the end of runout zones.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Avoid shallow snowpack areas where triggering is more likely.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 7

Valid until: Dec 15th, 2012 2:00PM