Avalanche Forecast

Archived

Dec 31st, 2018–Jan 1st, 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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Happy New Year! Human triggered avalanches were reported Monday from this zone resulting several near misses. Recent avalanches are a clear sign of the dangerous avalanche conditions. This is a good time to give avalanche terrain a wide berth and stay off of and out from under all slopes greater than 30 degrees.

Discussion

Avalanche and Snowpack Discussion

Monday was an active day in the Crystal backcountry. Avalanche were reported in Cement Basin, East Peak, Pickhandle Basin, Three-Way Pack, Sourdough Gap, Elk Pass, and Cash Run. Many of these were human triggered avalanches, including some remote triggers. These avalanches were generally large and acted in unusual ways. They failed on lower angle slopes, propagated widely, crossed terrain features, and occurred low in the startzones. Observations like this scream buried surface hoar.

12/31/18: A large avalanche that was remotely triggered in the Crystal backcountry. Photo: Jeremy Allyn.

We have not received observations from other locations in the West-South zone. That doesn’t mean that buried surface hoar isn’t there. Areas such as White Pass and Chinook Pass are likely areas to encounter a similar, weak snowpack.

Snowpack Discussion

New Regional Synopsis Coming Soon

Problems

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.

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.