Avalanche Forecast

Issued: Apr 5th, 2014 9:47AM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs, Deep Persistent Slabs and Loose Dry.

swerner, Avalanche Canada

Northwest Coastal.

Monday's storm will pack a punch and is driving the Danger Ratings. The snowpack does not typically handle rapid change well and deeply buried persistent weak layers may re-awaken.

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

Unsettled conditions bringing light to moderate precipitation amounts will persist through the weekend. On Sunday night an intense, direct frontal system will slam the North bringing heavy precipitation and rising freezing levels. Sunday: Freezing levels rising to 1000 m and expecting 10-20 mm. Ridgetop winds generally light from the south with strong gusts. Monday: Freezing levels rising to 1400 m and expecting up to 50 mm in coastal areas (Kasiks) and up to 30 mm inland (Bear Pass, Stewart, etc.). Ridgetop winds strong from the south gusting to extreme values. Tuesday: Freezing levels falling to 1000 m or lower. Precipitation amounts 10-20 mm in coastal areas with lower amounts near 10 mm as you move inland.

Avalanche Summary

The recent storm snow has shown a fairly poor bond to the older snow surfaces. Natural loose dry and wet avalanche activity up to size 2 was reported on Friday. Continued natural avalanche activity is expected at all elevations through the forecast period.

Snowpack Summary

Up to 30 cm new snow fell onto a mix of surface hoar, small grained facets, melt freeze crusts and firm wind pressed snow. The new snow seems to be bonding poorly to these older snow surfaces and isolated wind slabs have formed at upper elevations.Previous snow that fell between March 27-30th fell on top of a variety of old snow surfaces. I suspect the ongoing melt freeze cycles have largely healed any instabilities associated with this interface. Below treeline a spring-like snowpack exists including melt-freeze crusts and isothermal conditions. Two persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 - 100cm and is composed of facets/surface hoar on shady aspects and facets/crust on southerly aspects. The early February crust/facet/surface hoar combo is down 150 - 200cm. This layer was responsible for a couple of unexpected large avalanches right at the end of March and the beginning of April. These layers should be on your radar and could become reactive with intense loading from rain/snow, warm temperatures and strong winds that are expected during this forecast period.

Problems

Storm Slabs

New snow driven by strong ridge top winds has likely created touchy slabs at and above treeline. This snow adds to existing storm snow and is expected to be unstable especially on lee features.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid freshly wind loaded features.>Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Deep Persistent Slabs

Two buried weak layers exist in the snowpack. These weak layers could be activated by cornice fall, a smaller surface avalanche in motion, or a rider finding the sweet spot, which would be most likely in steep rocky terrain.

Be aware of the potential for large, deep avalanches due to the presence of buried facets and surface hoar.>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 7

Loose Dry

Loose dry avalanches are likely from steeper terrain features at higher elevations. Lower elevations below treeline where precipitation falls as rain, you can expect to see some loose wet avalanche activity.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Apr 6th, 2014 2:00PM