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Olympics

Issued: 8:08 PM PST Thursday, December 28, 2017
by Robert Hahn

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.

Human triggered avalanches will become more likely as denser storm snow continues to build over less dense older snow near and above treeline as snowfall intensities increase during the day Friday. Especially watch for building wind slab on a variety of aspects near and above treeline where either older less dense or newer denser snow has been transported onto lee slopes. As rainfall increases and moves to higher elevations tomorrow, watch for saturated snow and avoid consequential terrain features. Watch for changing conditions, travel conservatively and rein in your plans as conditions deteriorate throughout the day.

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Avalanche Problems for Friday

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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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:

At Hurricane Ridge, the frontal system arriving Thursday evening brought a few inches of higher density snow at temperatures just below freezing, with light to occasionally moderate SW winds which transported some snow.

This new snow sits over the estimated 6 inches of lower density snow accumulation during the series of weak weather disturbances that traversed the area over the last week prior to Thursday. 

The previous major storm cycle ended 12/19-12/20.

Observations

On Wednesday, a shallow loose dry avalanche on a northwest aspect in the Tunnel Path above the road ran 100 feet and knocked a skier off his feet. A pit nearby showed right-side-up snow.

A second hand report of at least one human triggered loose dry avalanche (sluff) caught a skier(s) on Sunday 12/25. No injuries were reported. 

NWAC pro observer Matt Schonwald was at Hurricane Ridge on Saturday 12/24 and reported evidence of north to east winds but no wind slab or significant layers in the upper snowpack. The snowpack structure was generally right-side with good bonds to the Thanksgiving crust.

Forecast for Friday:

A second storm (Friday) on the heels of the first (Thursday), will bring significantly more precipitation and further warming than the initial system. The storm track that will bring moderate SE winds shifting to SW during the day, along with further warming, increasing precipitation intensities, and snow lines rising above ridge crest level (at Hurricane) late in the day. Sharp cooling and drying should arrive during the evening hours.

Wind and storm slabs will be increasing in size and likelihood of human triggering as slabs of increasing thickness build over the lower density, weaker, older snow prior to Thursday and become increasingly touchy by later in the day. Especially watch for building wind slab on a variety of aspects as winds directions shift during the storm. Wind and storm slab issues will be confined to increasingly high elevations as the rain/snow line works it's way to higher elevations during the afternoon hours.

On Friday morning, loose wet avalanches are mostly likely encountered below treeline on steeper slopes due to warming and light to moderate rain. By afternoon, loose wet avalanches will be found further up the mountains in the near treeline band. At higher elevations which have received more snowfall, the loose wet slides will be larger and and increasingly consequential. In general, when snow is becoming saturated, avoid complex terrain as loose wet avalanches will be much more dangerous.

Watch for changing conditions, travel conservatively and rein in your plans if conditions deteriorate faster than expected. See the mountain weather tab for weather forecast details. 

Also despite all the 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

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.