Avalanche Forecast

Issued: Mar 29th, 2012 10:43AM

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

swerner, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Fair - Due to variable weather conditions

Weather Forecast

A continued low over the Gulf of Alaska will whirl a series of convective systems through the southern part of the province, bringing light precipitation to the North West regions. Friday: Snow amounts 5-15 cm. Ridgetop winds light from the SW. Alpine temperatures near -4. Freezing levels 900 m then falling to valley bottom at night. Saturday/Sunday: The weekend will continue with quite the mixed bag of unsettled, spring-like convective weather. Expect bands of fast moving clouds, light precipitation, and periods of sun in the afternoons. Freezing levels 500- 800 m during the day, falling to valley bottom at night. Ridgetop winds will be light - moderate from the SE.

Avalanche Summary

On Wednesday numerous point releases, and wet slab avalanches were reported. These occurred on isolated steep south aspects, up to size 2.5 below treeline elevations. Natural glide crack, slab releases also occurred below treeline up to size 3. Avalanche control with the use of explosives triggered several size 2-3 glide slabs, below 1000 m. The snowpack below treeline will remain unstable until the region receives a good re-freeze. Unsettled weather conditions are forecast. It's important to pay attention to weather, and it's influence on the snowpack when recreating in your local mountains. I suspect the period will be fairly cloudy, but if periods of sun shine through, beware of solar aspects.

Snowpack Summary

Moderate to strong southeast winds have created wind slabs on opposite slopes and terrain features in the alpine, and treeline. Spring-like conditions have existed over the past several days forming crusts on solar aspects at all elevations that become moist under sunny skies during the day. Melt conditions exist on all aspects below 1000 m, with no significant re-freeze. This has developed a well settled upper snowpack with no significant layers of concern. New surface hoar growth up to 10 mm has been reported on sheltered North aspects. Forecast snow may initially have a poor bond to these new surface forms (crusts, surface hoar). Below all this, down 60-120 cm exists a very spotty surface hoar/ facet interface. Operations from the field noted no recent activity on this layer. I suspect it's becoming dormant, but would be suspicious of large triggers like cornice fall, or under the weight of a sled and it's rider in specific areas. Cornices in the region are reported to be very large and potentially unstable.

Problems

Loose Wet

Mix sun & cloud, precipitation, and elevated freezing levels are creating an unstable snowpack below treeline. Pinwheels, moist snow, and natural avalanches are indicators of snowpack deterioration. Best to avoid slopes with these conditions.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Wind Slabs

Cranking, Southerly winds on Thursday will build wind slabs in unusual places. Expect them to be at all elevations on lee slopes, and terrain features. Cracking and/or whumphing felt below you is a good indicator of unstable, wind effected snow.

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Cornices

Cornices are reported to be very large and potentially unstable at this time. A cornice fall could be destructive by itself, and may also act as a trigger on the slope below.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 5

Valid until: Mar 30th, 2012 9:00AM