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Avalanche Forecast

Archived

Feb 19th, 2016–Feb 20th, 2016

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.

Regions

Olympics.

The avalanche danger should be greatest early Saturday following the storm Friday. Watch for wind loaded terrain and avoid steep slopes suspected of wind deposits. Conditions should improve as the snow pack slowly stabilizes through Saturday afternoon.

Detailed Forecast

Continued periods of light to moderate snow at cool temperatures, Friday night, along with strong winds.

This weather should build wind slabs on lee slopes near and above treeline. Watch for firmer wind transported snow, mainly on the lee slopes facing N to SE, below ridges. 

Heavier precipitation rates Friday night should increase the storm slab likelihood by early Saturday. 

Showers should end quickly early Saturday with partial clearing and diminishing winds. Cooler temperatures should continue Saturday. 

Watch for greater depths of storm snow and avoid wind loaded terrain and steep rollover features. 

Storm snow problems should improve through the day Saturday as upper snow layers settle and stabilize.

Snowpack Discussion

Weather and Snowpack

Dry weather with the warmest temperatures of the winter occurred February 7-10th with mild temperatures and high freezing levels. 

Rain and mild temperatures predominated Sunday and Monday with 1.5 inches of rain before a brief cooling trend brought a few inches of snow by Tuesday morning. Mild temperatures and windy conditions were seen on Wednesday.

Storm snow of 4-6 inches accumulated as of Friday afternoon 2/19 at cooler temperatures with strong winds.  

Recent Observations

Professional NWAC observer, Matt Schonwald was at Hurricane Ridge on Friday, Feb 19th. Recent storm snow deposits of about 4-6 inches had accumulated in wind sheltered locations. Very strong southerly winds where building shallow wind slabs on lee slopes near tree line below ridges and also building small cornices. No distinct layers were noted in the shallow new storm snow that was generally well bonded to the draining old wet snowpack. 

The main concern would be new snow instabilities, specifically new wind slab deposits, near and above treeline. Secondarily, small storm slabs, however, as of Friday afternoon, the storm deposits were insufficient to cause a significant danger increase.

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.