Avalanche Forecast

Issued: Dec 26th, 2011 8:23AM

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.

pmarshall, Avalanche Canada

South Coast.

Summary

Confidence

Fair - Timing of incoming weather is uncertain

Weather Forecast

A series of frontal systems will continue to affect the region over the next few days. In general, expect 15-20cm of snow each 12 hour period, with moderate to strong W-SW winds, and fluctuating freezing levels (FL). Tuesday: 15-30cm, heaviest in the evening/overnight. Strong SW winds, rising overnight. FL around 800-1000m gradually rising. Wednesday: 20-30cm, heaviest overnight. Strong W-SW winds. FL rising to 1600m. Thursday: 15-25cm. Strong SW winds. FL lowering to 1000m.

Avalanche Summary

Fresh wind slabs and cornices may be sensitive to human-triggers and the likelihood of natural activity will increase with the forecast weather.

Snowpack Summary

Wind-exposed slopes are predominately scoured and pressed, with pockets of wind slab from 20 to 50cm deep on North to East aspects at treeline and in the alpine.This new storm snow overlies a weak rain crust that formed last weekend. This crust extends to treeline elevations and overlies buried surface hoar and/or facets 10cm below. Generally speaking, confidence in this interface is growing, especially since it has'nt seen a significant load at the elevations where it exists. In the alpine where the crust does not exist, a stiffer wind slab may over-ride surface facets that formed during the early December dry spell. Persistent weaknesses seem to be less of a concern in the Cascades (Coquihalla and Allison Pass).The mid and lower snowpack are generally well-settled and strong.

Problems

Wind Slabs

Wind slabs have developed in exposed lee and cross-loaded terrain and may be quite reactive, especially where they over-ride last weekends rain crust or weak facets (sugar snow) from the early December dry spell.

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

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 5

Storm Slabs

Weaknesses may exist within or under the new storm snow. Natural avalanches will become more likely with each successive storm.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Valid until: Dec 27th, 2011 8:00AM