Avalanche Forecast

Issued: Apr 6th, 2014 10:07AM

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

swerner, Avalanche Canada

Northwest Inland.

Monday's storm could pack a punch and is driving the Danger Ratings. Persistent weak layers could possibly re-awaken, initiating large and destructive avalanches.

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

Starting tonight an intense, direct frontal system will slam the North Coast bringing moderate precipitation, strong to extreme southerly winds and rising freezing levels to the Inland Regions.Sunday night: Freezing levels rising to 900 m and expecting 20 cm of snow at upper elevations. Ridgetop winds strong from the southwest with strong gusts. Monday: Freezing levels rising to 2200 m and expecting up to 10-20 mm. Alpine temperatures near 5.0. Ridgetop winds strong from the south gusting to extreme values. Tuesday: Mix of sun and cloud. Freezing levels falling to 1100 m or lower. Ridgetop winds strong from the west.Wednesday: Mainly cloudy with some flurries. Ridgetop winds light from the west. Freezing levels near 11000 m.

Avalanche Summary

No recent avalanche activity has been reported. Last Tuesday a steep rocky NE facing feature at 1900m released naturally resulting in a size 3 avalanche. The possibility for large avalanches appears to be still there, and the chance of one is likely to increase with anticipated warming, and/ or localized new loads including precipitation and strong winds on Monday.

Snowpack Summary

A new storm slab will likely build with new snow accumulations though Monday. The new snow will add to the 20 cm that fell last Thursday onto a variety of old snow surfaces consisting of surface hoar, facets and melt freeze crusts. A poor bond likely exists.Previous snow that fell at the end of March seems to have settled and 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 possibly 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. While it's been mostly dormant, I would not rule out the possibility of it reawakening if we see prolonged warming and/or intense sunshine and new load from snow and rain.Check out the new Forecasters Blog post on warming and solar influences on the snowpack.

Problems

Storm Slabs

New snow driven by strong ridge top winds has likely created touchy slabs. The new snow is not expected to bond well to the current crust/surface hoar combo and will likely remain sensitive to natural avalanche activity.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

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 surface avalanche in motion, a rider finding the sweet spot, or new load from snow/ rain/ wind. Warming and solar influence is also a concern.

Be aware of the potential for large, deep avalanches due to the presence of buried facets and surface hoar.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 7

Loose Wet

With warmer temperatures, limited overnight re-freeze and rain forecast, loose wet avalanches are likely. A good indicator of weak snow is wet or moist surface snow, snowballing, and natural avalanches.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Avoid slopes when temperatures rise and the surface snow becomes moist or wet and shows signs of instability, like pinwheels and natural avalanches.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Apr 7th, 2014 2:00PM