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Avalanche Forecast

Archived

Feb 16th, 2014–Feb 17th, 2014

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Olympics.

A storm Sunday night is expected to cause high danger near and above treeline to last into Monday.

Detailed Forecast

Strong winds and snow showers will gradually decrease on Monday with cool temperatures.

New potentially deep storm slab will be likely on all sheltered aspects. New potentially deep wind slab will be likely on lee slopes. Natural or triggered avalanches should be likely especially near or above treeline on Monday. Avalanches may step down or reach the crust from Wednesday. Travel in avalanche terrain near and above treeline is not recommended on Monday unless you are sure the danger is less than expected.

Snowpack Discussion

Recent Northwest Weather

An extended dry mild period was seen the latter half of January. The was followed by very cold weather which produced low density snowfall and near surface faceted snow in early February. Now for the past 6 days the Northwest is getting pummeled by daily frontal systems producing periods of strong winds, periods of warmer higher density snowfall and rain during periods of generally warmer temperatures.

Water equivalents in the Cascades near and west the past 6 days are in the 3-7 inch range with snowfall in the 2-4 foot range. Less data is available for the Olympics but should be similar. Note this means there has to have been some rain or generally heavy wet snow the past 6 days.

Hurricane Ridge

At Hurricane this weather has been building deep new snow and a rain crust from Wednesday over colder lower density snow from early February in turn over surface hoar frost and a crust from late January.

A park ranger and NWAC observer Tyler Reid at Hurricane Ridge Friday reported one ski triggered D2 avalanche on a northeast slope at 5200 feet on Friday.

A snow profile at Hurricane Ridge over the weekend on a southeast slope had about 20 cm of F DF storm snow, over a 3 cm MF rain crust from last Wednesday, over 22 cm of F+ RG recent snow over 4F snow over crusts from January. Snow pit tests by Tyler on Saturday gave moderate to hard, SP results and potential to propagate on the MF crust.

Tyler gave us a video of the tests https://www.youtube.com/watch?v=XBqeIeqkGao

Limited snow at the lowest elevations will limit the avalanche danger there. The mid and base pack should still consist of mostly stable crusts and melt form layers from periods of warm weather earlier this winter.

The next very strong cold front will cross the Olympics and Cascades Sunday night. This will produce stormy weather with very strong winds, slight warming and then cooling, and heavy snowfall. An avalanche cycle is likely Sunday night.

 

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.