Avalanche Forecast

Archived

Feb 8th, 2019–Feb 9th, 2019

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 possible, human triggered probable.

Regions

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Expect very dangerous avalanche conditions on Saturday. Natural avalanches are likely at upper elevations as snow and strong winds form fresh slabs on old weak surfaces. Stay well out from under steep slopes and avoid avalanche terrain above treeline.

Discussion

Snow and Avalanche Discussion

On Friday, the North Cascades experienced a gradual shift to unstable weather with light snowfall, variable winds, and highs in the teens. The storm will intensify Friday night and Saturday. Several inches of new, low-density snow and gusty northeast winds will bring very dangerous avalanche conditions. Of most concern are shallow snowpack areas in the eastern portion of the zone.

The new snow will bond poorly to weak and variable old snow surfaces. We may be tracking this interface for some time into the future. Expect blustery conditions and fresh wind slab formation Saturday. This added load has the potential to wake up buried persistent weak layers. In wind-sheltered areas, loose dry avalanche concerns may also develop. The most dangerous conditions exist at upper elevations where travel in and below avalanche terrain is not recommended.

Surface hoar and weak facets blanketed many slopes as of Thursday. This could become a weak layer buried by the incoming storm. Photo Josh Hirshberg

Snowpack Discussion

Regional Synopsis Coming Soon

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.