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Olympics

Issued: 7:32 PM PST Thursday, February 22, 2018
by Dallas Glass

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. 

New shallow and wind slabs will form in the Olympics on Friday. Identify and avoid areas where the wind is actively depositing snow. Persistent slabs are still present in the Olympics. Avoid steep open slopes greater than 35 degrees where you are most likely to trigger this very difficult to manage avalanche problem.

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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:

New snow and moderate winds will cause the avalanche danger to increase slightly Friday, as slabs grow larger and become easier to trigger.

Fresh shallow wind slabs will form on lee slopes as winds increase. You will most likely trigger these avalanches on steep slopes below blowing snow, plumes, and fresh cornices. Identify and avoid steep terrain where winds are actively loading new snow.

In many locations a persistent weak layer exists within the snowpack. Around 2 feet of settled snow sits on top of weak sugary facets buried on 2/13. At least 2 avalanches have been triggered by backcountry travelers on this layer during the past week in the Olympics. Persistent slabs can be difficult to manage. They do not heal as quickly as other avalanche problems and can remain active for weeks at a time. Observations on where these weak layers are present and how easy they are to trigger is hard to obtain. Give youself a wide safety buffer to handle the uncertainty around persistent slabs. Avoid slopes greater than 35 degrees where this problematic avalanche concern is thought to exist.

Excellent travel conditions can still be found in lower angle sheltered terrain not exposed to steep overhead slopes.

Avalanche Summary:

Two feet of settled snow exist around the Hurricane Ridge area over the 2/13 weak layer in sheltered areas. In exposed terrain, winds have redistributed snow near and above treeline. Wind deposited snow can be found on a variety of aspects along ridgelines.

Weak old snow (facets) can be found above the most recent crust layer. In most locations this is 1.5-2.5 feet below the snow surface. Observations continue to indicate this layer is reactive and capable of producing large avalanches. This layer has been reported on all but due South aspects.

There are no other significant layers of concern in the mid and lower snowpack.

Observations

On Friday Matt Schonwald and NPS rangers observed 20-30 inches of generally right-side-up surface snow over weaker snow (facets). Snowpack tests indicated the weak facet layer could still fail and produce avalanches. Northeast winds during the day Friday redistributed snow onto SW-W-NW aspects.

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.