Avalanche Forecast

Issued: Mar 29th, 2012 10:19AM

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

swerner, Avalanche Canada

Northwest Inland.

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 3-10 cm. Ridgetop winds light from the SW. Alpine temperatures near -3. Freezing levels 1200 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 800 m during the day, falling to valley bottom at night. Ridgetop winds will be light - moderate from the SE-SW.

Avalanche Summary

Reports from Wednesday indicated loose, solar induced sluffing and pinwheeling below 1500 m. On Tuesday a natural cornice fall triggered a size 2 slab avalanche on the slope below. This occurred on a NE aspect.

Snowpack Summary

Moderate-Strong SE-S winds continue to build wind slabs. They may be found in unusual places, lower on the slope or in open areas below treeline. Windward aspects may become wind pressed, and even scoured. North aspects at higher elevations hold dryer, low density snow in the upper 20 cm. Spring-like conditions exist and crusts have formed on solar aspects at all elevations, becoming moist under sunny skies. Melt-freeze conditions exist @ treeline on all aspects. Below treeline has remained moist, with no recovery below 1500 m. The mid-pack is well consolidated. The mid February persistent weak layer, comprised of spotty surface hoar, facets and crusts, is buried 80-120 cm below the surface. No recent activity has been reported on this interface. It most likely needs a large trigger on a specific spot. If an avalanche occurs on this weak interface it will be very large and destructive. Below this the snowpack is well settled and strong. Cornices in the area are reported to be very large. Cornice failure could trigger an avalanche on the slope below.

Problems

Wind Slabs

Cranking, Southerly winds have built wind slabs in unusual places. Most likely found in upper elevations on lee slopes, and behind 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: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Loose Wet

Mix sun and cloud, with little overnight re-freeze below 1500 m may be the right recipe for loose wet avalanches. Natural avalanches, pinwheels, and moist snow 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

Cornices

Large cornices exist in alpine terrain. A failure could be destructive by itself, and could also trigger an avalanche on the slope below. Use extra caution if the sun shines through.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 5

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