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Avalanche Forecast

Archived

Apr 6th, 2014–Apr 7th, 2014

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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.

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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.