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Avalanche Forecast

Archived

Jan 9th, 2019–Jan 10th, 2019

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

Regions

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The Bottom Line: Even though the avalanche danger is slowly dropping you will still need to be heads-up Thursday. You may trigger avalanches in areas where the wind has formed firm slabs or in locations where weak old snow layers exist. You can stay safe by avoiding slopes greater than 35 degrees.

Snowpack and Avalanche Discussion

We have quite a bit of uncertainty around the weather forecast for the next 24 hrs. Weather models are struggling to determine freezing levels and precipitation amounts. This will add another layer of variability to an already variable snowpack in the East-Central zone. When conditions like this exist, it’s a good time to be heads-up. Is what you are seeing inline with the avalanche forecast? If not, stop and reevaluate. In general areas closure to the Cascade crest may exhibit features closer to snowpacks of Stevens and Snoqualmie Passes. Further east a much weaker and more complex snowpack exists.

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.