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Avalanche Forecast

Archived

Dec 9th, 2019–Dec 10th, 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 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

Glacier.

Weaknesses in the snowpack from late November may be difficult to trigger, but could produce very large avalanches. Conservative use of terrain is the best way to manage this problem.

Weather Forecast

A brief ridge gives cool and relatively stable weather for the next couple days. This will be followed by a pulse of precipitation mid week.

Today: Sunny periods. No precip. Treeline temps High -8 C. Light West winds.

Tonight: Mostly cloudy. TL temps Low -8 C. Light West winds.

Tuesday: Sunny periods. TL temps High -4 C. Light SW winds. Frzlvl 1300m.

Snowpack Summary

Moderate S-SW winds building fresh wind slabs in the alpine. 40cm of previous storm snow (since Dec. 5th) overlies surface hoar in some locations TL and BTL, and is concealing evidence of the recent cycle of natural avalanches. The November 23rd surface hoar/crust/facet layer is buried 80-100+cm and remains reactive in stability tests.

Avalanche Summary

Several large (up to size 2.5) natural avalanches were observed Saturday from steep terrain in the highway corridor.

Avalanche control Friday produced numerous size 3 and several size 3.5 avalanches.

Confidence

Due to the quality of field observations

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.