Avalanche Forecast

Archived

Feb 12th, 2019–Feb 13th, 2019

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

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The new snow buried variable and weak old snow surfaces. It will still be easy to trigger a large avalanche on Wednesday. The most dangerous conditions exist near and above treeline in areas where the wind drifts new snow.

Discussion

Snow and Avalanche Discussion

The Washington Pass area received over one foot of new snow (1in SWE) in the past two days, the majority of which fell overnight and during the day on Monday. The storm brought a slight warming trend and was accompanied by little wind. The new snow is very light, cold, and cohesionless in most areas. Snowfall should taper off overnight, light to moderate winds will continue to blow from the southwest, and skies may clear by the afternoon on Wednesday.

On Tuesday, observers reported shooting cracks, whumphing, and touchy slabs near ridge crest in the Washington Pass area. On Monday, a skier was able to trigger a small wind slab on a northeast aspect at 6,000ft. Throughout the North Cascades, we have received recent reports of avalanches and snowpack tests failing on southerly aspects on a layer of facets above a thin sun crust. An observer reported instabilities on a similar layer on southerly aspects near Washington Pass on Saturday. The new snow may rest atop facets in some areas, and in others, it may not. Recently it has lacked cohesion or a slab structure, but this may change Wednesday due to sun, continued settlement, and wind. Areas of slab are more likely to be found at upper elevations. In areas to the south, persistent slabs are beginning to wake up in a more widespread fashion with more recent snowfall and water weight. Take note - this incremental loading for the Northeast zone is a tricky pattern.

Most avalanche accidents occur with Considerable Danger. Continue to be aware of your surroundings and check for instabilities. Ask yourself, "Am I in avalanche terrain? Could the snow slide?" Traveling one at a time is good practice, but it does not eliminate the hazard of choosing to enter avalanche terrain. Stick to lower angle, supported terrain, and places well away from large, steep, open slopes.

Snowpack Discussion

New Regional Synopsis Coming Soon

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.

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.