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Avalanche Forecast

Archived

Dec 27th, 2014–Dec 28th, 2014

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

Regions

Olympics.

New wind and storm slab should be the main avalanche problems on Sunday. A surface hoar layer from Thursday night will increase instability where it gets buried intact.

Detailed Forecast

Decreasing northwest winds, decreasing light snow showers and a cooling trend should be the main story in the Olympics on Sunday. New snow should run in the 5-10 inch range at Hurricane.

The main avalanche problems Sunday should be new storm and wind slab.Storm slab will occur in areas that receive more than an inch of snow an hour for several or more hours. For wind slab watch for firmer wind transported snow on lee slopes. The surface hoar will increase instability where it gets buried intact. You can check for this layer using hand shear tests or shovel tilt tests. These problems are most likely in the near and above treeline where there is more snow cover.

A trend of decreasing danger should be seen on Sunday as new layers begin to stabilize. The trend of decreasing winds, decreasing light showers and cooling should also cause some nice right side up conditions on some sheltered slopes.

Snowpack Discussion

The Olympic zone is finally getting enough snow to warrant avalanche forecasts for the season! NWAC observer Tyler Reid confirmed on Friday there is now sufficient snow to produce avalanches and get someone in trouble if in the wrong spot.

A warm storm moved over the Northwest Tuesday and Wednesday with strong west winds followed by lowering snow levels. A few inches was probably seen at Hurricane at the tail end of the storm.

A cooler period with little precipitation was seen about Thursday to Friday. Surface hoar is possible from Thursday night.

Have a look at Friday's video by Tyler:

 A cold front is moving over the Northwest on Saturday and Saturday night causing west winds and moderate to heavy snow and snow showers in the Olympics and a cooling trend. This should build some new wind and storm slab by Sunday.

Problems

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.

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.