Avalanche Forecast

Issued: Nov 29th, 2012 9:47AM

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 - Intensity of incoming weather is uncertain

Weather Forecast

A deep low pressure system off the Gulf of Alaska will continue to bring moist, warm and an active weather pattern over the next few days. Weaker impulses embedded in the flow will bring moderate amounts of precipitation over the mountains. Timing of these pulses are tricky to predict. Friday: FLVL’s 1400 m, snow amounts 10-20 cm, ridgetop winds SE 40- gusting 60 km/hr, alpine temps -3.0.Saturday: FLVL’s 1200m, snow amounts up to 15 cm, ridgetop winds SE 40-50 km/hr, alpine temps -4.0. Sunday: FLVL’s 1000-1200 m, snow amounts 5-8 cm, ridgetop winds S 10 km/hr, alpine temps -4.0.

Avalanche Summary

No new observations today.Reports from the Whistler area on Tuesday include a Size 2.5 deep slab avalanche running on the early November facet/crust combo triggered with small explosives low on the slope. Check out Wayne Flann's Avalanche Blog for more information, including photos. Also of note, there was a report of a size 2.5 skier triggered avalanche on Saturday. This avalanche occurred on a northeast aspect in the alpine. It was triggered from the bottom of the slope, and likely released on the early November layer.Natural avalanche activity will be the theme over the forecast period.

Snowpack Summary

The region will continue moderate-heavy amounts of new snow, and strong winds. Storm slabs and fresh wind slabs will load a variety of weak surfaces. These (now buried) surfaces consist of large surface hoar, a thin sun crust, surface facets, moist snow, or preserved storm snow depending on elevation, sun and wind exposure, slope angle, time of day, and aspect. Below this, the mid-pack seems to be fairly settled, strong and bridging instabilities that may exist deeper.Under the mid-pack (80-130 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, 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 snow at upper elevations will build storm slabs on all aspects, overlying a variety of weak surface layers. Storm slabs, and new wind slabs will be touchy, and natural avalanche activity is likely with heavy loading from snow and strong SE wind.

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: Alpine, Treeline.

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.>Be aware of the potential for wide propagations if deeper instabilities are triggered.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Nov 30th, 2012 2:00PM