Avalanche Forecast

Issued: Mar 29th, 2012 10:43AM

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

swerner, Avalanche Canada

Cariboos.

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 residual dribs and drabs of those systems to the northern regions. Friday: Snow amounts 5-10 cm. Ridgetop winds light from the SW. Alpine temperatures near -4. Freezing levels 1200m. 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 look to behave at 1000-1100 m during the day, then falling to valley bottom at night.

Avalanche Summary

Natural avalanche activity seems to have tapered off over the past couple days. Most recent reports are of loose wet slabs (unknown size) below 1400 m. I suspect weather limited most operations from the field.Earlier this week the region saw many large cornice falls on N-E slopes. These did trigger smaller size 1-2 avalanches, but nothing stepped down to the deep persistent layer. This is good. Yet I wouldn't' rule out the potential, as we saw that layer reactive only 6 days ago. Numerous loose wet avalanches were also reported on Monday on various aspects, running up to size 2.

Snowpack Summary

Recently formed, variable wind slabs exist in the alpine, treeline, and open areas below treeline. These can be found on lee slopes, and behind terrain features. Over the past several days, spring-like conditions have influenced the snowpack. Solar radiation has led to moist surfaces on sunny slopes up to ridgetop during the day, and other aspects moist below 1500 m with limited crust recovery overnight. Cornices have grown large and may become unstable under sunny skies; they may act as a large trigger on slopes below. A well settled, 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

Wind slabs, and cornices will continue to build with forecast snow and SW winds.They exist on lee slopes, and terrain features. Whumphing felt below you is a good indicator of unstable snow. Cornices may become weak, and fail with afternoon sunshine.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

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: Alpine, Treeline.

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. The last incident occurred Saturday March 24th, don't rule it out yet.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

4 - 8

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