Avalanche Forecast

Issued: Dec 16th, 2011 10:02AM

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

jlammers, Avalanche Canada

Northwest Inland.

Summary

Confidence

Fair - Freezing levels are uncertain on Saturday

Weather Forecast

Between friday night and saturday morning 10-20cm of snow and moderate to strong southwest winds are forecast for the region. Freezing levels for this period are expected to rise to 1500m with a possibility of freezing rain at lower elevations.A clearing trend is forecast for saturday afternoon and into sunday morning as winds eventually switch to light and northerly and freezing levels fall to surface.The clearing will be short-lived as more heavy snowfall and strong southwest winds will resume on sunday afternoon and into monday. Freezing levels on monday to sit at about 800m.

Avalanche Summary

Several size 2 natural avalanches were reported earlier in the week. These occurred on northerly aspects failing on the SH/CR/FC combo layer. I suspect we will see a natural cycle through the early part of the weekend with more snow and wind forecast.

Snowpack Summary

A few centimetres of new snow and surface hoar crystals are sitting on the less recent 20cm of storm snow which fell earlier in the week. This storm snow we received earlier this week sits on a variety of old weak snow surfaces including surface hoar, melt-freeze crusts and facetted snow. For the most part all aspects between 900m-2000m have a hard melt freeze crust. This crust is widespread and is lingering in most start zones. This is the layer of concern as we receive more snow and wind Friday and Saturday. Above this crust surface hoar (feathery crystals) and facets (sugary crystals) may be preserved. This exists at treeline and below treeline elevations. The recent winds in the alpine seem to have destroyed the surface hoar in exposed areas eliminating that problem but creating a wind slab problem. These wind slabs are in the immediate lee of features, sitting on the SH/CR/FC combo. They are reactive and rider triggered avalanches are likely. The midpack seems to be well settled and strong. Thanks to those who have sent in field observations. If you have any info from the field, we would love to hear from you. Write to us at forecaster@avalanche.ca

Problems

Wind Slabs

Fresh, reactive wind slabs will continue to develop on lee and cross-loaded terrain in the alpine and at treeline.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Storm Slabs

Freezing levels and snowfall amounts are uncertain for the forecast period. If conditions line-up, expect reactive storm slab development throughout all elevation bands.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Dec 17th, 2011 8:00AM