Avalanche Forecast

Issued: Dec 1st, 2012 9:14AM

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

swerner, Avalanche Canada

Sea To Sky.

Summary

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain on Tuesday

Weather Forecast

The recent weather pattern continues, with a very persistent deep low off the coast driving a moist, mild SW flow over the region. Moderate accumulations are expected through the forecast period, accompanied by moderate S-SW winds. Sunday: Fzlvl’s 1200 m, snow amounts 5-10 cm, ridgetop winds SE 15-25 km/hr, alpine temps -4.Monday: Fzlvl’s 1200 m, snow amounts 8-15 cm, ridgetop winds S 35 km/hr, alpine temps -4.Tuesday: Fzlvl’s 1700 m in the am then falling to 900 m in the afternoon, snow amounts 10-15 cm, ridgetop winds S 30 km/hr, alpine temps -3 falling to -8.

Avalanche Summary

Explosive testing produced numerous size 1-1.5 slab avalanches on NW-N aspects. All instabilities reacting within the storm snow.

Snowpack Summary

Storm slabs and fresh wind slabs have loaded a variety of weak surfaces. These (now buried) surfaces consist of large surface hoar, a thin sun crust, and surface facets. Below this, the mid-pack seems to be fairly settled, strong and bridging instabilities that may exist deeper.Under the mid-pack (90-150 cm down) sits the early November facet/ crust persistent weakness. Recent snowpack tests have shown sudden collapse (or "drops") results on the early November facet/crust deep persistent weakness, but because this weakness is so close to the ground in most areas, any associated avalanche activity will likely be limited to slopes with smooth ground cover (e.g. scree slopes, rock slabs, summer firn, glaciers, etc.). Areas that are most susceptible to trigger this deep persistent weakness are shallow, thin and variable snowpack deposition spots.To view a recent snow pit profile from the Spearhead Range, check out the Wayne Flann Avalanche Blog.

Problems

Storm Slabs

New storm slabs and wind slabs are building at higher elevations. Natural and rider triggered avalanches are likely; especially on lee slopes, and behind terrain features that have been wind loaded.

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

Likely - Very Likely

Expected Size

1 - 5

Deep Persistent Slabs

Slopes with smooth ground cover and reloaded bed surfaces may be prone to remote triggering and step down avalanches. Typical trigger points include thin rocky areas. May be difficult to trigger, but often very large with serious consequences.

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 2nd, 2012 2:00PM