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Avalanche Forecast

Archived

Jan 11th, 2019–Jan 12th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

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The Bottom Line: You may be able to trigger life threatening avalanches in areas where weak old snow exists. The wind has formed firm slabs in some locations that are difficult to trigger, but still present danger. You can stay safe by avoiding slopes greater than 30 degrees.

Snow and Avalanche Discussion

With good weather in store for the weekend, it is likely that folks will be getting up high into the mountains. It is important to realize that there is much uncertainty with our persistent weak layers above 6,000ft, and a high amount of variability within the zone. The recent upslope storm revived winter on the eastern slopes and added a hefty load to the upper elevation snowpack. Snowfall totals vary widely, from 5" to 14", with more at higher elevations. A common structure to be found out there will be storm snow (with or without a wind slab) over a crust. Recent wind slab avalanches at Mission Ridge were from 6" to 16" deep and from 60' to 125' wide, running on this crust. One that started on a Northwest aspect at 6300ft broke into older, weak snow near the ground. At low elevations and on southerly aspects, the snow surface has a thin crust from light rain or sun, and a number of loose wet avalanches were observed.

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.