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Avalanche Forecast

Archived

Nov 29th, 2016–Nov 30th, 2016

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.

Regions

Olympics.

New storm and wind slabs may locally become a concern in areas that experience intense snowfall rates Wednesday. Watch for potentially increasing avalanche danger in the afternoon and be prepared to change your plans if conditions warrant.  

Detailed Forecast

A weak frontal system passing through the Olympics early Wednesday morning should bring light amounts of new snow above 3500 feet. Brisk westerly winds Wednesday should also build fresh wind slabs on lee easterly aspects.

New storm and wind slabs may locally become a concern in areas that experience intense snowfall rates Wednesday. Watch for potentially increasing avalanche danger in the afternoon and be prepared to change your plans if conditions warrant.    

In much of the below treeline band there is not enough snow yet for avalanches.  Avalanche problems should be limited to the upper part of this elevation band.

 

Snowpack Discussion

A great report was received via the NWAC Observations tab for Saturday for the Hurricane area. In summary pit tests gave only a low quality shears or collapses and an ECT test that did not indicate any propagation. Loose dry avalanches were indicated as the main concern.

On Sunday morning the Hurricane rangers reported 7 inches of new snow. They reported that a snowboarder on Saturday triggered a small loose dry snow avalanche on the Sunrise run, a steep slope that faces northeast at about 5200 feet.

No observations were submitted on Monday but another 4 inches accumulated above 5000 feet in the Hurricane Ridge area with generally light WNW winds recorded at the NWAC weather station. Tuesday was a break between weather systems. 

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.

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.