Avalanche Forecast

Issued: Dec 29th, 2011 10:20AM

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

Avalanche Canada pgoddard, Avalanche Canada

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

Thursday night: 10-15cm snow. Freezing level 900m.Friday: 5-10cm snow. Freezing level rising briefly to around 1300m near the coast, then falling back to 900m. Strong westerly winds.Saturday: A cool sunny day. Sunday: Dry but mild, with cloudy periods possible.

Avalanche Summary

Numerous Size 1-3 slab avalanches (both natural and human triggered) have been reported in the past 72 hours. Skiers accidentally triggered avalanches in Garibaldi Park (Wednesday) and in the backcountry near Blackcomb (Thursday). In both cases they had a lucky escape. I expect to see continued avalanche activity; however we are getting into a period where there will not be as many obvious clues of danger: natural avalanching will decrease but human-triggering will probably increase.

Snowpack Summary

Around 20cm snow fell last night bringing the total snowfall in the past week to 100-170cm. Wind slabs have formed in exposed NW-E facing slopes, probably as deep as 100cm in some areas. Cornices have grown large and could act as a trigger for large avalanches. A weak rain crust is found below the new snow up to treeline elevations. This crust may sit on top of buried surface hoar and/or facets. One observer near Whistler reported whumpfing on a buried surface hoar layer in low-angle terrain below treeline. Watch this layer as it gets more load and a thick cohesive slab develops, particularly below treeline where the buried surface hoar would be especially large. A strong mid pack overlies basal facets that have also gained considerable strength. On average the snowpack is around 200cm deep near treeline.

Problems

Wind Slabs

An icon showing Wind Slabs
Deep and dense wind slabs exist below ridge crests, behind terrain features and in cross-loaded gullies.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 6

Storm Slabs

An icon showing Storm Slabs
Weaknesses are likely within or under the new storm snow and may be triggered naturally (loading from new snow or wind) or by the weight of a person. Storm slabs could also trigger deeper persistent weaknesses.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 6

Valid until: Dec 30th, 2011 8:00AM