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

Issued: 6:00 PM PST Thursday, April 26, 2018
by Josh Hirshberg

See the NWAC Spring Schedule 2018  for details on avalanche forecast products for the remainder of the season.

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.

Very warm temperatures and sun will create dangerous avalanche conditions on Friday. You can trigger large wet avalanches and cornices. Plan your travel to be out of avalanche terrain before afternoon.

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Avalanche Problems for Friday

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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Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.

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Wet Slabsi

Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.

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Forecast for Friday:

The avalanche danger will increase to Considerable by late Friday morning. Due to very warm temperatures and strong sun, you can trigger large wet avalanches. Plan your day to be out of avalanche terrain before the snow becomes wet and unsupportive.

You can easily trigger Loose Wet avalanches on most slopes over 35 degrees. Use extra caution on large, steep, and unsupported slopes where you may be able to trigger a large avalanche.  If you sink in wet snow up to the top of your boots, avoid slopes over 35 degrees. Wet Slabs can be dangerously large and are difficult to predict. These avalanches may be difficult for a single person to trigger, but could occur naturally with cornice fall. Wet snow resting on a weak layer or crust is a sign that you can expect Wet Slab conditions. Limit your exposure to large start zones and overhead avalanche paths suspect for Wet Slab avalanches.

Give cornices a wide buffer. They will break naturally and you could easily trigger them. Cornices will often break surprisingly far back from the edge. Make sure you are well off and out from under cornices, especially as the sun is shining on them. Cornice fall could be big enough to kill you and could trigger other avalanches.

Avalanche Summary:

A long stretch of warm weather and strong sun has ushered in spring-like avalanche concerns. An extensive cycle of Loose Wet avalanches and cornice falls occurred this week throughout the Cascades. As the warm temperatures have continued loose avalanches have been moving to higher elevations and more polar (northerly) aspects. Slab avalanche activity due to warming has been occurring, though not as widespread or showing major patterns.

Generally, Wet Slabs or slab avalanches entraining wet snow in the past week have occurred in the upper snowpack with a few deeper releases reported. On Thursday, avalanche workers on Washington Pass triggered multiple slab avalanches up to size 2.5. on north and east aspects around 7,500ft. Nearby, in the Mt Baker area and North Cascades National Park west of the Cascade crest observers have reported a significant cycle of slabs 3-6 feet (1-2 meters) deep. One observer reported probing a widespread weak layer 3 meters below the surface on the Silver Glacier. There have not been similar reports on the east side of the crest.

On Thursday, Forecaster Dallas Glass reported a natural cornice fall as well as easily triggering Loose Wet avalanches near the Alpental Valley. Dallas reported that a thin surface crust quickly softened in the morning.


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.