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

Issued: 6:03 AM PST Friday, March 2, 2018
by Josh Hirshberg

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. 

While the Avalanche Danger is slowly decreasing, dangerous conditions remain at upper elevations. You can trigger Wind Slabs near and above treeline and Persistent Slab avalanches on sunny slopes in the upper snowpack. Avoid wind loaded areas and large open sun-exposed slopes 35 degrees and steeper. 

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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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Persistent Slabi

Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.

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Forecast for Friday:

You can easily trigger Wind Slab avalanches near and above treeline, today. You can avoid these avalanches by staying off of recent snow drifts, deeply pillowed features, and fresh cornices on slopes 35 degrees and steeper. These areas may exist far below ridge-lines and on mid-slope cross-loaded features. In some location soft non-wind-effected snow may cover new wind slabs making them harder to identify. You may encounter some small loose avalanches releasing on the surface of steep slopes today. 

You can trigger Persistent Slab avalanches in the upper snowpack on sun-exposed slopes greater than 35 degrees. Avoid steep, open, sunny slopes as well as large avalanche paths to reduce your risk of these difficult to manage avalanches. If you dig about 2 feet below the surface you will find a series of thin sun crusts surrounded by very small facets. These layers have been the source of several avalanches in the Cascades. Snow profiles and snowpack test can confirm the presence of this layer; however they cannot prove its absences.

Observers continue to report potential for a Deep Persistent Slab. Avalanches triggered in the surface snow could step down to release a large and dangerous avalanche in deeper layers in the snowpack. These avalanches are becoming increasingly difficult to trigger. The best way to avoid this low likelihood-high consequence problem is by avoiding triggering smaller avalanches in the surface snow and staying out of large avalanche paths.

Avalanche Summary:

The Rainier and Crystal Mountain area picked up over a foot of snow since Wednesday and about 3 feet in the past week. Strong west and southwest wind accompanied much of the snow. Observers in the Crystal Mountain backcountry reported natural and triggered avalanche activity of many flavors since Sunday. Significantly more avalanche observations have come from this area in the past three days than other parts of the West Slopes.

On Thursday, Forecaster Dallas Glass reported natural slab avalanches in wind loaded terrain near treeline. Dallas reported test showing potential for triggering avalanches on crust/facet combinations in the upper snowpack as well as up to 3 feet down on the older faceted 2/13 layer.

NWAC professional observers in the Crystal area Tuesday and Wednesday observed the 2/23 interface, involved in two previous avalanches, still reactive in snowpack tests. In this area the 2/23 layer was found 1-2 feet below the snow surface.

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.