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Avalanche Forecast

Archived

Feb 20th, 2014–Feb 21st, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Snoqualmie Pass.

Recent deep snow layers will need a little time to stabilize.

Detailed Forecast

The amazing storm cycle of the past 10 days is winding down. Winds should decrease and light snow showers should end on Friday with cool temperatures. But deep avalanche layers will not go away right away.

This weather will start to bring some stabilizing to recent snow layers. The main concerns near and west of the crest will be recently formed wind and storm slab layers.

Deep wind slab will be mostly likely on lee slopes at higher elevations. Watch for signs of firmer wind transported snow. Deep storm slab will be left in the forecast for Friday in case it needs another day to stabilize. Deep storm slab should still be possible on Friday on sheltered aspects from above to below treeline.

Snowpack Discussion

Recent Northwest Weather

An extended mild and dry period occurred the latter half of January generally causing a crust to form in all areas. Very cold weather followed in early February which produced low density snowfall, periods of strong east winds in the Cascades, and strong temperature gradients in the upper snowpack that generally caused surface hoar frost and faceting near the crust.

During the past 10 days the Pacific Northwest has been pummeled almost daily by frontal systems producing periods of strong winds and heavy snowfall. The latest storm Wednesday night and Thursday morning has brought another round of heavy snow. Water equivalents in the Cascades near and west of the crest over the past 10 days are 9-14 inches with snowfall in the 6-11 foot range at NWAC weather stations.

Observations for Washington Cascades near and west of the crest

Several avalanche cycles have been seen the past 10 days. West of the crest the January crust has become buried pretty deeply and although some recent avalanches have been big it seems there isn't any confirmed activity down to that layer lately. Forecast attention near and west of the crest will be focused on recent storm layers.

A cold front Tuesday evening caused heavy loading rates at gradually warming temperatures. This caused a widespread natural avalanche cycle that was observed in many areas by Wednesday morning with numerous wind and storm slab avalanches noted from the Mt Baker, Snoqualmie Pass and Crystal Mountain ski areas. Some of the avalanches were up to 3-5 feet deep!

NWAC observers Jeff Hambelton and Dallas Glass on Wednesday near Mt Baker and Snoqualmie reported wind and soft slab layers in the recent deep snow.

Check out the latest video observation from NWAC observer Dallas Glass in the Snoqualmie Pass area Wednesday.

Another front moved past on Wednesday night and Thursday morning causing denser snow at warmer temperatures. Easy ski triggering of storm slabs on Thursday up to about 1-1.5 feet mainly on lee slopes was reported by ski areas including Mt Baker and Alpental. Paths were rapidly reloading at Alpental.

The mid and base pack should still consist of mostly stable crusts and melt form layers from periods of warm weather earlier this winter.

Note that persistent slab has been added as a concern east of the Cascade crest. Be sure to read the forecast for that area if you venture even slightly east of the crest.

Keep an eye on your riding partner in the deep snow until the new snow settles and the risk of SIS subsides. 

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.