Avalanche Forecast

Issued: Mar 28th, 2012 10:15AM

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

Avalanche Canada swerner, Avalanche Canada

Summary

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 Friday into Saturday. Thursday: Snow amounts near 5-10 cm. Ridgetop winds strong from the South, potentially blowing over 100km/hr. Alpine temperatures -4, freezing levels near 1100 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

On Tuesday, numerous reports of loose wet avalanche activity occurred. These all occurred on solar aspects up to size 2. Explosives control (using 75kg charges) produced several avalanches up to size 2.5. West aspects were targeted, at 900 m. These did run to ground surfaces, and left up to 2.5 m of debris on the road. 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. I expect this to continue through Thursday with cranking Southerlies all day. Spring-like conditions have existed over the past several days. This has formed crusts on solar aspects at all elevations that become moist under sunny skies during the day. Melt-freeze conditions exist on all aspects below 1000 m. 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

Wind Slabs

An icon showing 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

Likely

Expected Size

1 - 4

Cornices

An icon showing 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 - 6

Loose Wet

An icon showing 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 29th, 2012 9:00AM