Avalanche Forecast

Archived

Feb 11th, 2019–Feb 12th, 2019

Alpine

Natural avalanches possible, human triggered probable.

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

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This bitter cold, stormy pattern will continue to produce low density snow along with instabilities for Tuesday. We are tracking a recently buried persistent weak layer that has been found on a variety of aspects. This layer may produce wide avalanches and they may triggered from a distance. Seek out slopes less than 33 degrees if you find slab structure over facets. Storm slabs and fresh wind slabs may be sensitive at all elevations.

Discussion

Snow and Avalanche Discussion

Morning update: Considerable Danger all elevations

Avalanche danger is once again on the rise as a strong system lifts northward this afternoon into Tuesday. A series of strong and cold storms continue to roll through, mainly to the south of the area. On Monday a skier was able to trigger a small wind slab on a Northeast aspect at 6,000ft. On Sunday, a handful of slides were reported from near Baker on southerly aspects. One, a D2, was at 5,200ft on a steep Southwest aspect. It was triggered remotely by a skier. Investigated by a pro observer, it was found to have failed on a layer of facets above a thin suncrust. An observer reported instabilities on a similar layer on southerly aspects near Washington Pass on Saturday. The new snow may lie over facets in some areas, and in others it may not. Recently it has lacked cohesion, or a slab structure, but it may begin to get there with the new snow and wind overnight. Areas of slab are more likely to be found at upper elevations, where the wind has more influence above the trees. In areas to the south, persistent slabs are beginning to wake up in a more widespread fashion with more snowfall and water weight. Take note. This incremental loading for the Northeast zone is a tricky pattern.

Most avalanche accidents occur with Considerable Danger. Maybe we weren't truly there on Monday. However, as the snow continues to lightly pile up, 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. Slopes of less than 30 degrees, and places well away from steep open slopes would be my preferred terrain choice.

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.