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Avalanche Forecast

Archived

Dec 31st, 2018–Jan 1st, 2019

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

Regions

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The Bottom Line: Happy New Year! Sunshine and cool weather will usher in the New Year, but avalanches are happening in unusual ways, so it’s not a time to be complacent. You may still trigger avalanches in wind loaded areas. In some locations wind deposited snow may sit on a layer of weak buried surface hoar. If you experience collapsing, cracking in the snow, or see recent avalanches, avoid open slopes 30 degrees or steeper.

Avalanche and Snowpack Discussion

Several natural and human triggered avalanches were reported in the adjacent north zone in Schrieber’s Meadow and Heather Meadows areas on Sunday. Many of these avalanches were unusual. They propagated widely, had thin crowns, released low on the slope, and/or failed on lower angled slopes. When we see signs like this, it calls attention to buried surface hoar. Human triggered avalanches in other zones have failed on a similar layer.

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.