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Olympics

Issued: 6:05 PM PST Thursday, March 8, 2018
by Robert Hahn

The avalanche danger will increase during the day on Thursday as a storm system impacts the Olympics. Look for developing Wind Slabs on lee slopes near and above treeline that you can easily trigger. There is uncertainty around the potential for large Persistent Slab avalanches. Until we receive more information, reduce your risk by avoiding open slopes 35 degrees and steeper. Rainfall will increase the likelihood for Loose Wet avalanches below treeline. 

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Avalanche Problems for Thursday

Wind Slabi

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Persistent Slabi

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Loose Weti

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Forecast for Thursday:

The avalanche danger will increase during the day on Thursday as a storm system brings light to moderate rain and snow to the Olympics along with windy conditions. Look for developing Wind Slabs on lee slopes near and above treeline that you can easily trigger. Watch for cracking, wind stiffened snow, and freshly formed drifts. Steer around fresh wind features, convex rolls, and slopes holding a foot or more of new, cohesive snow that are 35 degrees and steeper. Shallow Storm Slabs may develop by the afternoon in less wind affected terrain.

Although it is becoming unlikely, you may still be able to trigger Persistent Slab avalanches on slopes 35 degrees and steeper. We think this problem is decreasing in the Olympics because we have no reports of recent avalanche activity. Facets (weak snow) have not been found to be widespread. However, variability exists across the terrain and persistent slabs have proven to be quite dangerous in the nearby Cascades so reduce your risk by avoiding steep, open slopes and large avalanche path and dig down and check for weak sugar-like facets or buried surface hoar above the most recent firm crust layer formed in early February on all but south aspects before engaging with avalanche terrain. This crust layer is down about 2-4 feet. 

The rain/snow line is forecast to rise to 4000-5000' Thursday. Rainfall will raise the likelihood of small Loose Wet avalanches on steep slopes below treeline, especially those that have received fresh snowfall. Avoid steep slopes below treeline connected to terrain traps, where even a small Loose Wet avalanche could have unintended consequences. 

Avalanche Summary:

Temperatures at Hurricane Ridge pushed above 40F Wednesday with high overcast skies. This likely moistened the snow surface on all aspects in the Hurricane Ridge area.

On shaded aspects, about 3 ft of settled snow sits a strong crust formed in February. In some areas, weak faceted snow was found above this crust. We do not have recent observations on the distribution or likelihood of triggering an avalanche on this interface. There are no other significant layers of concern in the mid and lower snowpack.

A very different and very shallow snowpack exists on south-facing aspects where warm temperatures and sunshine prior to mid-February melted the majority of the snowpack. Much of the snow on south-facing was deposited from mid-February onwards. Basal facets were present on the ground on southerly aspects and this will be something to watch if warm temperatures haven't healed this interface prior to the incoming storm.

Observations

On Saturday March 3rd, NPS rangers found 2-3 mm buried surface hoar from mid February intact on a NNW aspect at 4990’. The surface hoar was about 4" (10 cm) above a crust 32" (80 cm) below the surface. No new or recent avalanche activity was observed on this layer. The snow depth was much shallower on due south slopes (as little as 1.5 ft deep, recent snow only) as compared to northerly slopes (120" deep). On south-facing aspects, the total snow was 1.5' deep and 1-2 mm basal facets were present on the ground.

On Friday, March 2nd, NPS rangers reported a large avalanche on a recently wind loaded slope. Elsewhere, profiles showed a faceted weak layer buried in mid- February was found 2-4 feet below the surface and was showing some signs of rounding.

No Corresponding Mountain Weather Forecast Available
This information is provided by the U.S.D.A. Forest Service and describes general backcountry avalanche hazard and conditions. It does not apply to ski areas and highways where avalanche mitigation is conducted. Read more here.