Avalanche Forecast

Issued: Mar 27th, 2012 10:28AM

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

swerner, Avalanche Canada

Cariboos.

Summary

Confidence

Fair - Due to variable weather conditions

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 5-15 cm above 1200 m. Ridgetop winds moderate from the SW. Freezing levels 1500 m. Thursday: Snow amounts 8-15 cm. Ridgetop winds strong from the SW. Freezing levels 1600-1800 m. Friday: Light bands of precipitation, and cloud cover.

Avalanche Summary

On Monday several large natural solar induced cornice releases were reported. These occurred on NW-NE slopes from 2000 m- 2400 m. To note, none of theses cornice falls stepped down to the deeply buried persistent weak layer. I still wouldn't rule out the potential, as we saw that layer reactive only 4 days ago. Numerous loose wet avalanches were also reported on Monday on various aspects, running up to size 2. This could continue in your local mountains if the sun is able to poke through the clouds over the next few days. On Saturday three, size 3 natural avalanches were observed in steep, rocky, unsupported terrain. They occurred between 2000-2800m on north to east aspects and are suspected to have run on the February persistent weak layer.

Snowpack Summary

Recently formed variable wind slabs exist in the alpine and at treeline. Over the past several days, spring-like conditions have influenced the snowpack. Solar radiation has led to moist surfaces on sun exposed slopes up to ridgetop, other aspects moist below 1500 m. Crust recovery developing at night. Cornices have grown large and have become unstable; they may act as a large trigger on slopes below. A consolidated slab overlies a persistent weak layer that was buried in early February. Now 1-2 m below the surface, these weaknesses include surface hoar, facets or crusts. Concern still exists potentially for deep and destructive releases at this interface. This may be a low probability, high consequence problem that may require a large trigger.

Problems

Wind Slabs

New wind slabs will form with forecast snow and moderate SW winds. These 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

Likely

Expected Size

1 - 4

Cornices

Large cornices exist and may fail. Cornice fall could be detrimental in itself, stay well back on ridgelines, and slopes below. A cornice fall provides a large trigger, and could initiate an avalanche on the slope below.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 5

Deep Persistent Slabs

A weak interface down 1-2 m remains concerning. While avalanches on this layer have become less frequent, those that do release are very large and destructive.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

4 - 8

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