Avalanche Forecast

Issued: Nov 24th, 2011 9:01AM

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

ccampbell, Avalanche Canada

Sea To Sky.

Avalanche danger is expected to increase as another intense storm hits the coast.

Summary

Confidence

Fair - Due to limited field observationsfor the entire period

Weather Forecast

Friday: Mostly cloudy with flurries bringing 3-5cm. Freezing levels around 500m, and strong northwesterly winds becoming westerlies late in the day. Saturday: A warm intense Pacific frontal system brings heavy precipitation, extreme southwesterly winds, and freezing levels as high as 2000m in the afternoon. Total accumulations are expected to be in the 50-100cm range by Sunday afternoon. Sunday: Freezing levels are expected to drop to 1000m, winds calm down and shift to westerlies, and precipitation is expected to ease off throughout the day.

Avalanche Summary

Recent human-triggered whumpfing and large remote avalanches were reported to be associated with the mid-pack crust/facet complex at upper treeline and lower alpine elevations. I suspect newly formed wind slabs will be very touchy.

Snowpack Summary

There's been over a metre of new snow since Sunday. Fluctuating freezing levels and varying wind and precipitation intensity during the recent storms has probably resulted in various storm snow weaknesses. There was also widespread large surface hoar observed on the previous snow surface at all elevations. A persistent weakness of facets, with an associated crust at upper treeline elevations, can be found down 70-150cm. This weakness seems to be particularly touchy between 1800 and 2000m where it is very sensitive to human triggers and has a high propensity to propagate fractures. Buried surface hoar has also been spotted just below this crust, and sitting on top in some locations. A deeper crust with associated facets and/or depth hoar is approximately 50cm off the ground.

Problems

Persistent Slabs

Particularly touchy where there is an associated rain crust, which is prominent between 1800m and 2050m. Potential for remote triggering means that even low-angle terrain may not be safe if there is exposure from above.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 6

Wind Slabs

Newly formed weak wind slabs are likely lurking well below ridgecrests and terrain breaks, and in cross-loaded gullies.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

2 - 5

Storm Slabs

Any open slope with enough snow to smooth out ground roughness. Various weaknesses with and under the recent storm snow are likely sensitive to human triggers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Nov 25th, 2011 8:00AM