Avalanche Forecast

Issued: Feb 23rd, 2012 8:42AM

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

Avalanche Canada pmarshall, Avalanche Canada

A Special Public Avalanche Warning has been issued for this region for February 24-27. Current conditions are very touchy and require extremely conservative decision making.

Summary

Confidence

Good

Weather Forecast

Friday: Light to moderate snow beginning in the morning - 5-10cm. The freezing level (FL) is near valley bottom. Ridge top winds should be moderate from the SW. Saturday: Continued moderate snowfall - an additional 10-15cm overnight and through the day. FL rising to 800m. Winds should ease to light from the west. Sunday: Unsettled conditions with convective flurries likely. FL drops to valley bottom. Winds are light and variable.

Avalanche Summary

A natural avalanche cycle occurred on Wednesday in most areas. Slab avalanches were reported up to Size 2.5 on all aspects and at all elevations. There were also several reports of skier triggered avalanches and remotely triggered avalanches up to Size 2.0, and a Size 2 snowmobile triggered avalanche near Blue River. The potential for triggering large avalanches will remain high throughout the forecast period.

Snowpack Summary

Wind slabs continue to grow in exposed terrain in response to moderate SW-NW winds. 30-60cm of storm snow has now settled into a cohesive slab and overlies the Feb. 9 weakness, which includes surface hoar and/or a crust. This surface hoar layer may be widespread in some areas, while others have reported it being confined to shady aspects at treeline and in the alpine. A melt-freeze crust can be found down 50-70cm on solar aspects at all elevations, and on all aspects below about 1600 metres. In some areas this melt-freeze crust has facets above or below it. The mid-pack is generally well settled. There is some concern that large loads like cornices may trigger the Jan. 20th facet layer. Some shallow snowpack areas may continue to have a weak layer of basal facets near the ground.

Problems

Wind Slabs

An icon showing Wind Slabs
Strong southwest-northwest winds have created deep wind slabs overlying several persistent weaknesses in the upper snowpack.

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

Elevations: Alpine, Treeline.

Likelihood

Very Likely - Certain

Expected Size

2 - 6

Persistent Slabs

An icon showing Persistent Slabs
Up to 70cm of settling storm snow overlies several weaknesses including surface hoar and a sun crust. It may be possible to trigger avalanches in surprisingly low-angle terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 6

Valid until: Feb 24th, 2012 8:00AM