Avalanche Forecast

Issued: Dec 2nd, 2012 9:20AM

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

swerner, Avalanche Canada

South Coast.

Summary

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

A broad upper trough remains just offshore while a cooler, unstable onshore flow will persist and strengthen through Monday. On Tuesday an embedded frontal system will bring heavy amounts of precipitation, rising freezing levels and strong SW winds hammering the region. Wednesday the flow will switch from SW to NW, and precipitation amounts will ease up.Monday: Fzlvl’s 1000 m, snow amounts 5-10 cm, ridgetop winds S 30, alpine temps -6.Tuesday: Fzlvl’s 1700 m in am falling to 700 m, snow amounts 15-20 cm, ridgetop winds SW 30-gusting to 70 km/hr, alpine temps -4.Wednesday: Fzlv l’s 700 m, snow amounts near 5 cm, ridgetop winds S 30 km/hr, alpine temps -9.

Avalanche Summary

No new avalanche observations have been reported. With strong winds and heavy precipitation forecast for Tuesday, expect avalanche danger to be on the rise with natural avalanche activity likely.

Snowpack Summary

Storm slabs and new wind slabs will load a variety of weak surfaces and be touchy. These surfaces consist of large surface hoar, a thin sun crust, surface facets. The new snow may have a poor bond to these underlying weaknesses. Below the surface, the mid-pack seems to be settled and bridging over the early Nov facet/crust. However, near the bottom of the snowpack under the crust exists large, low density faceted crystals. The storm (loading) on Tuesday will provide a good test on this basal weakness.Snowpack tests from earlier this week showed sudden collapse results on the early November facet/crust deep persistent weakness. Because this weakness is so close to the ground in most areas, associated avalanche activity will likely be limited to slopes with smooth ground cover (e.g. scree slopes, rock slabs, summer firn, glaciers, etc.). Be aware of triggering this layer from thin, rocky areas, this persistent weakness my be a low probability/ high consequence scenario.

Problems

Storm Slabs

Storm slabs and wind slabs are overlying a variety of weak surfaces. With continued loading, natural avalanche activity can be expected. Rider triggers are likely; especially on wind loaded lee slopes, gullies, and over convex rolls.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Persistent Slabs

Typical trigger points include shallow variable snowpack depths, and thin rocky areas. Difficult to trigger, but often result in very large and destructive avalanches. Suspect terrain: offers a smooth ground cover (scree, grassy, rock slabs etc.)

Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Dec 3rd, 2012 2:00PM