Avalanche Forecast

Issued: Mar 20th, 2013 9:49AM

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

Avalanche Canada Peter, Avalanche Canada

Summary

Confidence

Good

Weather Forecast

Synopsis: Cooler and unsettled conditions are expected for Thursday and Friday. A ridge of high pressure should start to develop on Friday resulting in drier and sunnier weather.  Thursday: Mainly cloudy with a chance of flurries. The freezing level drops to valley bottom overnight and winds are moderate from the northwest. Friday and Saturday: A mix of sun and cloud. The freezing level drops to valley bottom overnight and rises to 800 m during the day. Winds are light to moderate from the north-northwest.

Avalanche Summary

On Tuesday morning there was a report of a size 2.5 skier triggered avalanche in the Blackcomb backcountry. Check out Wayne Flann's Avalanche Blog for photos and details from this incident. Fortunately everyone involved was rescued successfully.There have been a few other reports of rider triggered avalanches up to size 2 in the past couple days. Most have been from northerly aspects in the alpine or at treeline. There was also a report of a size 3 cornice triggered avalanche on Monday, highlighting the potential for large avalanches.

Snowpack Summary

An additional 30-50 cm of snow has fallen in the past 48 hours, accompanied by very strong southeast-southwest winds and rising freezing levels. Temperatures are forecast to drop rapidly in the wake of the system. This will probably result in a solid refreeze below treeline. However, the new snow may still remain sensitive to triggering at higher elevations, especially in wind loaded terrain. Below the recent new snow lies one or two weak layers buried approximately 60-80 cm below the surface. These comprise faceted snow, surface hoar and/or a crust. The snowpack structure is quite variable at this time. It may change dramatically with only a subtle change in elevation, aspect, wind or sun exposure. Mid and lower snowpack layers are well bonded.

Problems

Storm Slabs

An icon showing Storm Slabs
It may be possible to trigger slabs in steep terrain or on convex shaped slopes, particulary at and above treeline. Watch for deep wind slabs on Northwest through East aspects behind ridges and terrain features and in cross-loaded gullies.
The new snow will require several days to settle and stabilize.>Choose well supported terrain without convexities.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Cornices

An icon showing Cornices
Cornices are reported to be very large at this time. They are a danger in themselves, but could also trigger a slab avalanche on the slope below.
Give cornices a wide berth when travelling on or below ridges.>Do not travel on slopes that are exposed to cornices overhead.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 21st, 2013 2:00PM