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Olympics

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. 

Significant uncertainty exists in the Olympics right now so it is a good time to make conservative terrain choices. Identify and avoid steep wind-loaded slopes Friday where you will be able to trigger a wind slab avalanche. A Persistent Slab avalanche problem likely persists in the Hurricane Ridge area, but a lack of recent observations requires travelers to avoid open slopes where this difficult to manage problem may exist. Watch for extended direct sunshine on steep south facing slopes that may cause Loose avalanches.

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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 trigger Wind Slab avalanches at upper elevations. Today, you are most likely to trigger them above treeline. You can avoid these avalanches by staying off of recent snow drifts, deeply pillowed features, and fresh cornices on slopes 35 degrees and steeper. In some locations soft non-wind-effected snow may cover new wind slabs making them harder to identify. These areas may exist far below ridge-lines and on mid-slope cross-loaded features.

You can trigger Persistent Slab avalanches in the upper snowpack on shaded slopes greater than 35 degrees. Avoid steep, open slopes and large avalanche paths to reduce your risk of these difficult to manage avalanches. Weak sugar-like facets can be found just above a firm crust layer formed in early February on all but south aspects. This layer is down about 2-3 feet, shallow enough to be human triggered or triggered by a wind slab stepping down to the weak layer.

A series of thin sun crusts surrounded by very small facets has been observed in the Cascade Passes. These layers have been the source of several avalanches earlier this week. Snow profiles and snowpack test can confirm the presence of this layer; however they cannot prove its absences. It is uncertain if this persistent layer exists in the Hurricane Ridge area. 

Due to a lack of recent observations and a complicated snowpack, this is a good time to make conservative terrain choices.

Avalanche Summary:

Winds Wednesday night formed new wind slabs on a variety of aspects near and above treeline. In sheltered areas generally soft unconsolidated surface snow exists.

In the Cascades on E-S-W aspects, a thin breakable sun crust formed early last week and was buried on 2/23. Very small weak facets have been reported surrounding the crust. This was the weak layer found or suspected in several avalanches 1.5-3 feet deep. This layer has not yet had significant time to heal. It is found 2-3 feet below the surface on steeper slopes that have received direct sun during the past week. It is uncertain if this layer exists in the Hurricane Ridge area, but it seems consistent with the recent weather.

Some observations suggest other persistent grains at this same interface on shaded slopes. Buried surface hoar and large preserved stellars have been reported in recent avalanches and snowpack tests at this interface.

An active storm cycle began a week ago Friday. By Monday morning about 2 ft of new snow had accumulated in the Hurricane Ridge area.  

About 3 or more ft of of settled snow sits on top of the weak sugary facets that formed on a strong crust earlier in February. Snowpack tests continue to suggest that these facets can fail and produce avalanches. This layer has not been reported on South aspects in the Hurricane Ridge area.

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

Observations

No recent observations since Monday. 

NPS ranger Monday morning reported the most recent 9 inches of new snow at Hurricane Ridge had surprisingly little wind effects and was low cohesion.

Sunday, NPS rangers indicated the additional new 8 inches of snow was stiffer and more cohesive, being deposited over the previous days weak snow.

On Thursday, Feb 22, 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 Thursday 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.