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East Slopes North - Canadian Border to Lake Chelan

Issued: 6:00 PM PST Wednesday, December 7, 2016
by Garth Ferber

NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.

 

A lot is going to start happening on Thursday and regional timing of weather and avalanche conditions will be tricky.

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Avalanche Problems for Thursday

Wind Slabi

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

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Loose Dryi

Loose dry avalanches exist throughout the terrain, release at or below the trigger point, and can run in densely-treed areas. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells.

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Snowpack Analysis:

Weather and Snowpack

Active snowy weather has been seen so far in December. Most stations along the east slopes had about 1-1.5 feet of snow so far in December through Tuesday morning with an overall cooling trend.

Cold fair weather has been seen the past couple days. There have been many reports of right side up, favorable density profiles with lower density snow nearer the surface. We've been hearing the term "as good as it gets" quite a lot lately!

Given the favorable snowpack profile, good bonds of older snow layers and a lack of deeper layers of concern, avalanche problems should be confined to the most recent storm snow at this time.

Cold fair weather like this usually causes some new surface hoar layer and near surface faceted snow. This snow can make for great skiing or riding. But these layers will need to be watched if loaded by wind transported snow or new snow.

Recent Observations

During midweek last week NWAC pro-observer Jeff Ward was in the Washington Pass area and found generally good ski conditions and a stable snowpack. Stubborn and shallow wind slab existed near and above treeline.

The most recent observations from near Washington Pass Monday and Tuesday indicate great skiing, favorable snowpack profiles and good bonds of older snow layers.

While coverage in most below treeline remains thin, the upper elevations of this lowest band are filling in quite impressively and we are bumping the overall danger to moderate in this band as a result. But the lower elevations in many areas lack good coverage and open creeks and other early season hazards remain. 

In general, more snow is needed in the Mission Ridge area and southeast Cascades to present an avalanche danger. In wind-loaded terrain near and above treeline, no weak layers of note have been reported lately by the Mission pro-patrol.

Detailed Forecast for Thursday:

A lot is going to start happening on Thursday and regional timing of weather and avalanche conditions will be tricky.

Southeast winds at exposed locations in the Cascades should continue to increase Thursday in advance of an incoming front.

Watch for wind transport and new wind slab on unusual southwest to northeast aspects on Thursday due to southeast and east winds. Regionally it doesn't sound like there is much if any old wind slab out there so the southwest to northeast aspects along the east slopes will be highlighted for new wind slab on Thursday. But watch for firmer wind transported snow on all aspects since confidence is not high on which aspects to highlight. The slight warming trend could enhance the formation of new wind slab on Thursday.

The front with increasing snow and a slight warming trend should begin to lift south to north over the Northwest starting in the south at Mt Hood by Thursday afternoon and reaching the Olympics and Washington Cascades by Thursday night. Be prepared to change your plans if the front and significantly increasing snow arrives earlier than expected along the east slopes during the day on Thursday.

In steep sheltered terrain Thursday continue to watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences.

Even though the lower part of the below treeline band is filling in, you will need to watch for early season travel hazards such as barely covered rocks and open creeks.

Further new wind and storm slab likely Thursday night. The warming trend should enhance the formation of these layers.

Observations