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Olympics

Avalanche Warning i

Issued: Thu, March 9, 2017 at 8:35 PM PST
Expires: Thu, March 9, 2017 at 6:00 PM PST

Issued: 8:35 PM PST Thursday, March 9, 2017
by Dennis D'Amico

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.

Numerous serious avalanche involvements occurred in the Olympics and Washington Cascades over the March 4th-5th weekend. NWAC has posted brief summaries of the incidents here: http://www.nwac.us/accidents/accident-reports/. Full reports will be posted when finished. 

Due to the potential for large avalanches in many areas following Thursday's complex storm, travel in avalanche terrain is not recommended on Friday. Allow the recently stressed snowpack time to settle and stay out of consequential terrain. 

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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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Storm Slabsi

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

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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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Snowpack Analysis:

Weather and Snowpack

The most recent warm, wet storm arrived on Valentines Day 2/14 forming a strong rain crust, now buried 3 feet or more in the Hurricane Ridge area.

Strong southwest flow carried a strong front across the Northwest on Friday evening March 3rd. This caused strong southwest alpine winds and heavy, moist, dense new snow above about 3-4000 feet. A region wide avalanche cycle was seen late Friday March 3rd and Saturday March 4th.

The NPS ranger on Thursday morning reported 10 inches of snow received over the last 3 days at Hurricane Ridge.  Increasing snow with rising temperatures and S winds were seen Thursday afternoon at Hurricane Ridge. 

Recent Observations

Reports by NPS rangers early Sunday 3/5 and a report listed on the NWAC Observations page indicates there were at least three and possibly four separate triggered avalanches in the Hurricane Ridge area Saturday 3/4, including the areas known as Maggies, Hurricane Hill and Sunrise Face.

Detailed Forecast for Friday:

Dense snow received in the Olympics Thursday afternoon should be followed by a period of rain Thursday evening up to 6000 feet and then by light showers with a slow cooling trend during the day on Friday. S-SW winds will increase Thursday night and stay strong through Friday morning.

With a complex weather pattern afflicting the Olympics and Cascades Thursday and Thursday night and stressing our deep storm snow received over the last week, travel in avalanche terrain is not recommended on Friday. Allow the recently stressed snowpack time to settle and avoid consequential terrain. Realize that large avalanches are possible if initially small avalanches step down to deep and lingering storm instabilities or if a large natural trigger like a cornice collapse occurs. 

Deep wind slab should be suspected on all aspects near and above treeline but most likely found on NW to SE aspects due to recent SW to W winds. Watch for firmer wind transported snow on varied aspects especially in areas of complex terrain.

Storm slab should still be sensitive on Friday due to denser storm slab building over weaker snow received earlier in the storm and potentially stepping down to deeper storm layers from earlier in the week.   

Loose wet avalanches are possible below treeline if moderate rain showers occur Friday. Loose wet avalanches that begin small may become large by entraining deeper layers.

Cornices won't be listed as an avalanche problem but avoid travel on ridges near where cornices may have formed and avoid steep slopes below cornices that may fail at any time. Cornices have been reported as large and in charge in many areas. They will have likely been weakened during the recent storm cycle becoming more likely to fail. 

No Corresponding Mountain Weather Forecast Available