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Avalanche Forecast

Archived

Dec 7th, 2017–Dec 8th, 2017

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

Regions

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Lack of observations from this region will require greater assessment of conditions by the back country travelers. Above treeline is mainly where there has been enough snow for wind to transport snow and form wind slab. Be especially wary of small loose wet avalanches near terrain traps. 

Detailed Forecast

Expect some high clouds and slightly cooler temperatures on Friday with light winds at higher elevations. The inversion conditions should also continue with some low clouds and much cooler temperatures in passes and at lower elevations.

Above treeline is mainly where there has been enough snow for wind to transport snow and form wind slab. Newer wind slab may be found on west-facing aspects and older wind slabs may be seen on more usual northwest to southeast aspects. Older wind slab should become increasingly stubborn, while newer, fresher wind slabs may be more reactive. Watch for areas of wind-scoured slopes which transport snow onto lee features and avoid the latter. These slabs will generally be small due to the limited amount of snow available for transport.

Snow on steep solar slopes should have mostly slid or consolidated in sunny warm weather on Thursday. Any high clouds and slightly cooler temperatures should diminish the danger of loose wet avalanches on Friday. But continue to watch for loose wet snow on steep solar slopes especially near sun warmed terrain features.

Lack of observations from this region will require greater assessment of conditions by the backcountry traveler.

Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.

Snowpack Discussion

Warm, wet weather before Thanksgiving caused first storm, then wet snow avalanches in the Washington Pass area.  Post-Thanksgiving about 2 feet of snow accumulated in the Washington Pass area and this amount has settled above the Thanksgiving Day crust.

A series of frontal systems produced snow over the week following Thanksgiving at all stations in the Cascades: Locations on the east side of the Cascade crest had about 5-15".

The most recent snowfall ended early Sunday. 

Dry and cool conditions Sunday and Monday allowed for snowpack settlement and allowed recent storm layers to begin stabilizing. Warm and sunny weather Tuesday to Thursday at higher elevations allowed for further consolidation and some moist surface snow on solar aspects.  Inversions have been firmly established on Wednesday and Thursday, with much cooler temperatures present at Washington Pass base (not making it out of the mid-20's) than the upper Washington Pass site in the 40's. Winds have light at some locations such as Washington Pass but moderate east winds have been seen such as at the top of Dirty Face Peak near Lake Wenatchee.

Observations

North

No recent observations.

Central

Last Saturday, backcountry professionals skiing at Ingalls Peak reported generally stable conditions with some small, unreactive wind slab.

A report via the NWAC Observations for the Teanaway-Hawkins Mtn area for Wednesday indicated a new crop of surface hoar, stabilizing wind slab and a couple small loose wet avalanches on steep solar slopes.

South

No recent observations.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.