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Avalanche Forecast

Archived

Feb 8th, 2015–Feb 9th, 2015

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

Regions

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A heightened avalanche danger will mainly be limited to steep open terrain or lee slopes above treeline.  

Detailed Forecast

Warming is expected Monday with periods of light to moderate rain and snow with generally light to moderate winds. Rain near and below treeline should maintain some wet surface snow conditions, making triggered small loose wet avalanches possible on steeper slopes.

At the highest elevations, generally above 6000 feet, some building storm or wind slab is expected. These areas of storm or wind slab may build on isolated terrain features, such as lee aspects near ridges, mainly NW through NE facing. 

Do note as a result of the unseasonably low snowpack, especially at lower elevations, numerous terrain hazards such as open creeks, partially covered rocks and vegetation are widespread.  

Snowpack Discussion

Periods of light snowfall occurred this week east of the crest at higher elevations with more snowfall at higher elevations in the northeast and central east zones. The snow level stayed about 5500 feet in the northeast Cascades for most of Thursday night with snowfall accumulation likely in the 6-10 inch range in the Washington Pass area before likely mixing with light rain Friday. Much less new snow was reported in the Stuart range and Mission Ridge area above 6500 feet Friday.  Slight cooling with a frontal system Saturday deposited an additional about 2-4 inches of snow above about 4-5000 feet as of Sunday. Warm daytime temperatures and some sunshine Sunday likely settled or melted recent new snow.  

Observer, Tom Curtis traveled to Dirty Face peak above Lake Wenatchee Saturday where shallow wet snow was accumulating above about 4800 feet and some small storm and wind slabs where developing through the day near and above treeline. Wet snow avalanches were possible below treeline.  There were no natural avalanches or instabilities observed with minimal wind slab developing along ridges from 5400 feet and above. The mid January crust layer we have been tracking was now poorly defined with no results from several stability tests performed. The new storm snow was only a few inches an was limiting the avalanche potential. 

NWAC pro-obs and North Cascade Guides, report last week in the northeast and central east zones have the January 15th facet/crust layers at 40 cm-1 m below the surface with the facets starting to turn to rounded grains and not reactive or not releasing in pit tests. It thus appears the January 15th facet/crust layers are strengthening and stabilizing. This problem has been removed from the central east zone forecast, but retained in the northeast zone until more information becomes available following this storm cycle.

Jeff Ward was in the Stuart Range Friday and found small but sensitive, loose wet avalanches naturally and skier triggered above about 6500 ft. Below this elevation, there was not enough new snow for wet loose danger and the most recent crust had not significantly softened. In the area traveled, the rest of the pack was consolidated and the Jan 15th layer was non-reactive in snowpit tests.

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.