Snoqualmie Pass

Issued: 6:20 PM PST Saturday, December 30, 2017
by Kenny Kramer

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.

Significant new snow and strong winds over the last several days continue to warrant patience and conservative terrain use. The snowpack is slowing gaining strength, but caution should be taken before stepping into larger terrain.

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Avalanche Problems for Sunday

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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Storm Slabsi

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

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Avalanche Summary:

Saturday afternoon brought a close to a wet and wild storm pattern which began on Thursday. East flow in the passes maintained cooler temperatures, allowing for mostly snow throughout the storm systems. Snoqualmie pass did receive short rain, and freezing rain events Friday during the day, but the passes did not receive the same warm temperatures experienced across much of the west slopes of the Cascades.

One to two feet of snow fell from Thursday to Saturday afternoon. Temperature fluctuations during the storm created several layers within the new snow. Settlement and strengthening of the upper snowpack can be seen in weather station data and has been confirmed by recent field observations.

Moderate winds associated with the end of the storm cycle have redistributed snow in exposed terrain, creating newly formed wind slabs on a variety of aspects.

The upper snowpack is generally right-side-up and gaining strength. Freezing rain and freezing fog crust buried 12/29 and 12/28 respectively exist in the Snoqualmie pass area. The extent of these crusts is not well known.


Stevens Pass

On Friday, a professional guide in the Stevens backcountry reported a resistance increase within the 15" of storm snow and that storm snow was bonding well with the old snow interface. The layers were not producing significant test results.

Snoqualmie Pass

On Friday, the WSDOT crew at Snoqualmie Pass reported numerous small loose wet avalanches on steep NW-facing terrain and at that elevation there was not much snow to entrain.

On Friday, Alpental Pro Patrol reported evidence of a natural cycle from 1' of storm slab in the early morning hours on Friday. The snow switched to rain and rain was reported to the top of Alpental by late morning.

Forecast for Sunday:

Easterly flow will continue to bring cooler temperatures and low elevation clouds to the Passes Sunday.

Newly formed wind slabs will continue to be a problem into Sunday. Look 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 has occurred. Strong ridge top winds may have loaded slopes well below ridgeline.

While we expect wind slabs to primarily exist near and above treeline, keep a watchful eye out for exposed terrain features below treeline where wind slabs may have formed.

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.

With the lack of significant warming in the Passes, Storm Slab instabilities will continue to linger into Sunday. While these layers are settling and gaining strength, the shear amount of new snow warrants caution. Avalanches originating within the new snow may entrain additional snow from lower layers. Storm slabs will have the potential to be their largest at higher elevations where significant new snow loads and colder temperatures exist.

The snowpack is quite deep in many locations. Small trees can present a non-avalanche, snow immersion hazard. Keep visual and verbal communication with your travel partners when traveling in treed terrain.

Despite all this new snow, early season hazards still exist at some lower elevation locales and especially around creek beds that are not filled in.

No Corresponding Mountain Weather Forecast Available


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.