Archived

Avalanche Forecast

Mar 28th, 2012–Mar 29th, 2012

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Northwest Inland.

Confidence

Fair - Due to variable weather conditions

Weather Forecast

A continued low over the Gulf of Alaska will whirl a series of convective and synoptic systems into the southern part of the province, bringing remnants of those systems to the northern regions. The bulk of the precipitation will arrive Thursday-Friday, with continued bands of fast moving clouds, light precipitation and sunny breaks later into Saturday. Thursday: Snow amounts near 5 cm. Ridgetop winds strong from the South. Alpine temperatures -4, freezing levels near 1200 m during the day then dropping to valley bottom at night. Friday: Snow amounts 5-10 cm. Ridgetop winds moderate from the South. Freezing levels valley bottom. Saturday: Occasional light flurries and cloud cover. Sunny breaks expected with intense solar radiation during those times. Freezing levels are expected to be near 600 m.

Avalanche Summary

Reports from Tuesday indicated small loose, solar induced sluffing. A natural cornice fall triggered a size 2 slab avalanche on the slope below. This occurred on a NE aspect. Other operations have reported no new avalanche activity through their tenures.

Snowpack Summary

Wind slabs will continue to build. 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 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. 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.

Avalanche Problems

Wind Slabs

Cranking, Southerly winds on Thursday will build wind slabs in unusual places. They may be found 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: 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 - 5

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