Avalanche Forecast

Issued: Nov 28th, 2012 9:24AM

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

Fair - Intensity of incoming weather is uncertain

Weather Forecast

A deep low pressure system off the Gulf of Alaska will be bringing a very moist, warm and active weather pattern over the next five days. The system will move into the region Wednesday afternoon, and persist with moderate to heavy amounts of precipitation through the weekend. Thursday: FLVL’s 1500 m, snow amounts up to 30 cm, ridegtop winds SE 40-gusting 70 km/hr, alpine temps -2.0.Friday: FLVL’s 1400 m, snow amounts 15-25 cm, ridgetop winds SE 60-gusting 90 km/hr, alpine temps -3.0.Saturday: FLVL’s 1400 m falling 1000 m overnight, snow amounts heavy, ridgetop winds S 20 kn/hr, alpine temps -3.0.

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. Widespread natural avalanche activity will be the theme over the forecast period.

Snowpack Summary

The region will see heavy amounts of new snow, and strong winds. Storm slabs will load a variety of weak surfaces. These 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. A storm snow instability has been noted down 30 cm, giving consistent moderate "pops" results in snowpack tests. Snowpack tests continue to show 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.).

Problems

Storm Slabs

Heavy amounts of new snow will build storm slabs on all aspects, overlying a variety of weak surface layers. Storm slabs, and new wind slabs will be touchy, and widespread natural avalanche activity is likely with heavy loading from snow and wind.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 4

Deep Persistent Slabs

Slopes with smooth ground cover and reloaded bed surfaces. 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.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Nov 29th, 2012 2:00PM