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West Slopes South - South of I-90 to Columbia River

Issued: 8:45 PM PST Tuesday, January 2, 2018
by Dennis D'Amico

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.

845 PM: Corrected east slopes of the Cascades 

Shallow wind slabs may linger in wind exposed terrain above treeline while small loose wet avalanches are possible on steep solar slopes. In some areas, firm surface crusts will make for difficult travel conditions so be prepared to self-arrest and think about the sliding hazard before crossing steeper slopes.  

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Avalanche Problems for Wednesday

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 Weti

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

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Avalanche Summary:

Mild weather seen Sunday through Tuesday has allowed lingering wind slabs to gain strength. Temperatures have been cooler in the Passes due to easterly flow, initially slowing the pace of stabilization in these areas.  

Regional temperature and wind variability during recent high pressure and offshore flow

Winds Saturday formed shallow slabs on a variety of aspects near and above treeline. Depending on elevation these wind slabs sit on soft snow storm snow or firm rain crust. Shallow wind slabs were triggered by recreational skiers on Sunday in the Snoqualmie and Mt. Baker backcountry. 

The Dec 28th/29th storm cycle formed a rain and/or freezing rain crust throughout the west slopes of the Cascades including the Passes that reached at least into the near treeline elevation band. A few inches to a foot of snow fell at the tail end, with the most snow at Mt. Baker. 

These firm crusts capped storm snow which fell earlier during the storm cycle. Below the 12/30 crust (date the crust was buried), a generally strengthening snowpack can be found. Weather stations from across the region confirm the upper snowpack is settling.

Observations

North

On Saturday and Sunday Mt Baker Pro Patrol reported wind transportation of the new snow at the upper elevations forming small shallow slabs. Evidence of rain was found to the top of the ski area.

NWAC pro observer Lee Lazzara was on Bear Paw Mountain Saturday. Lee reported a variety of snow surfaces conditions due to recent wind transportation of snow. He observed wind slabs up to 2 ft thick sitting on a firm rain crust formed during the overnight rain event.

Central

On Sunday, Stevens Pass Patrol described a freezing rain event to the top of the ski area that occurred Friday night. Winds Saturday formed shallow wind slabs within the area. Approximately 4” of soft snow sits above the freezing rain crust in wind sheltered areas.

Also on Sunday, Alpental Patrol reported a ½” freezing rain crust to the top of the ski area.

South

On Sunday, Crystal Mt Ski Patrol saw pockets of wind slabs at higher elevations. Friday’s rain crust extended to 6500’ in the ski area.

On Saturday NWAC Pro Observer Jeremy Allyn was in the Crystal backcountry. He observed evidence of rain in the form of a breakable rain crust all the way to ridge crest (6500’). Recent winds had redistributed the overnight snow forming pockets of wind slabs on lee slopes. Jeremy noted that variable snow surface conditions exist due to the recent wind event.

Forecast for Wednesday:

After a cloudy start, partly to mostly sunny skies are expected Wednesday afternoon with continued mild temperatures. The exception once again will apply to the Cascade Passes with cooler temperatures and areas of low clouds due to continued offshore flow. 

Lingering wind slabs should be far less sensitive to triggering on Wednesday and confined to higher terrain. Continue to watch for areas of recently wind transported snow such as fresh cornices, snow drifts, and uneven snow surfaces. Identify and avoid locations where recent wind loading occurred.

Wind slabs can be deceptively difficult to manage in the terrain. Take a moment and read our recent blog post by NWAC Pro Observer Jeremy Allyn on wind slabs.

Small loose wet avalanches are possible on steep solar slopes in areas that experience warm temperatures and afternoon sunshine on Wednesday. Be aware of the consequence of even a small loose wet avalanche around terrain traps.  

Cornices along ridge crest in the west slopes of the Cascades and Passes have grown quite large especially at higher elevations. Remember to give these features a wide berth. Cornices can break much farther back from the ridge than expected.

In some areas, firm surface crusts will make for difficult travel conditions so be prepared to self-arrest and think about the sliding hazard before crossing steep slopes.  

Despite all this new snow, early season hazards still exist. Many creek beds have still not filled in for the winter.

No Corresponding Mountain Weather Forecast Available

USE AT YOUR OWN RISK

This Backcountry Avalanche Forecast is provided in conjunction with the US Forest Service, and is intended for personal and recreational purposes only. Safe backcountry travel requires preparation and planning, and this information may be used for planning purposes but does not provide all the information necessary for backcountry travel. Advanced avalanche education is strongly encouraged.

The user acknowledges that it is impossible to accurately predict natural events such as avalanches in every instance, and the accuracy or reliability of the data provided here is not guaranteed in any way. This forecast describes general avalanche conditions and local variations will always occur. This forecast expires 24 hours after the posted time unless noted otherwise.