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Avalanche Forecast

Archived

Jan 1st, 2020–Jan 2nd, 2020

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

Regions

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Expect to find avalanche conditions that increase the higher you go. Recent new snow and strong winds have created dangerous slabs at higher elevations. Careful consideration is warranted before entering steep slopes in the alpine. 

Discussion

Over 1.25" of snow water equivalent fell at Washington Pass, adding 9" to the total snowpack depth at 5,400ft. Westerly winds were steady and strong, and likely created thick slabs on exposed slopes. A cycle of large natural avalanches was reported further to the west, off the Shuksan Arm on Wednesday. We don't yet know what the storm did in the Washington Pass and greater Northeast Cascades vicinity. If you get out, let everyone know what you find by submitting an observation.

 

 

Snowpack Discussion

New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.

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.