Avalanche Forecast

Issued: Mar 27th, 2012 10:26AM

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

swerner, Avalanche Canada

Northwest Inland.

Summary

Confidence

Good

Weather Forecast

A series of Pacific frontal waves and upper troughs will bring continued unsettled weather through the forecast period. Light -moderate precipitation amounts can be expected daily. With fast moving systems, timing seems to be hard to pinpoint. A strong upper SW flow will provide warmer the normal temperatures, rising freezing levels in the afternoon, then falling during the night. Things should start to cool off significantly by Friday. Wednesday: Snow amounts 5-10 cm. Ridgetop winds moderate from the South. Freezing levels 900-1000 m. Thursday/Friday: Light precipitation both days. Ridgetop winds mod-strong from the SW. Freezing levels 900 m, falling to valley bottom. on Friday.

Avalanche Summary

On Monday, 1 natural cornice failure triggered a slab avalanche size 2 on the slope below. This was on a NE aspect around 1300 m. Other operations have reported no new avalanche activity through their tenures.

Snowpack Summary

Moderate southerly winds have formed wind slabs in the alpine, and at treeline on lee and cross-loaded terrain. 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 below treeline on all aspects. Below this sits a well consolidated, settled mid pack. 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, although I feel that triggering may be possible in steep, isolated terrain in some parts of the region. 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

Variable wind slabs found in the alpine and at treeline. These may exist on lee aspects, 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.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Cornices

Large cornices exist in alpine terrain. A failure could be destructive by itself, and could also trigger an avalanche on the slope below.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 6

Loose Wet

Forecast mix sun and cloud could provide enough solar radiation to initiate loose wet avalanches on solar aspects. Snowballing, pinwheels, and moist surface snow are indicators of snowpack deterioration. Best to avoid slopes with these conditions.

Aspects: North, North East, East.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 28th, 2012 9:00AM