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Olympics

Issued: 5:50 PM PST Wednesday, November 22, 2017
by Robert Hahn

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.

Due to the current wet and mild conditions, the first regular Avalanche Forecast will now be issued Friday evening, valid for Saturday November 25th. The full winter forecast schedule will follow through mid-April. 

Poor and generally wet snow conditions are expected Thursday.  Loose wet avalanches are still possible in steeper terrain. Dangerous wet slab avalanches or glide avalanches are again possible in isolated areas on Thursday and may be favored in the Cascade Passes and locations east of the crest. If you decide to be in the backcountry, remember that even small wet snow avalanches are powerful and dangerous, especially near rock faces and terrain traps.

Carefully evaluate new storm and wind slab layers as they develop in the Olympics and Northwest Cascades on Friday near and above treeline.

Snowpack Analysis:

Avalanche and Weather Summary

Valid Thursday and Friday November 23-24

Normally, mid to late November is our wettest/stormiest period and mother nature is not disappointing.  Unfortunately this most recent round of wetness has mostly come in the form of rain with over 1-5 inches of water at most NWAC precipitation sites the last 48 hours!  

The continued warm and wet conditions have further melted and compressed the snowpack in most locations, now exposing bare ground in some locations which appeared to have a robust snowpack just a few days ago! From Tuesday morning through Wednesday morning, snow depths declined 6-17" in locations west of the Cascade Crest and the Olympics and 0-6" at most stations east of the Cascade Crest and Stevens/Snoqualmie passes. The exception to the snowpack decline has been the northeast Cascades, where a cold air pool enabled 1-3" of snow depth increase. The warm temperatures have now spilled into the northeast and temperatures at most locations here are now above freezing, so even these locations are now in snowpack decline.

Warming through the storm cycle at different stations throughout the Cascades:

Observations

Observations have been limited to ski areas and DOT crews over the past few days.

Mt. Baker ski area reports continued heavy rain as of Wednesday afternoon, with lots of climax activity on steep, rock slopes, all aspects, wiping out trees up to a foot in diameter with slides up to 100’ across inside ski area and on Shuksan arm. 

As of Wednesday morning, Mission Ridge Ski area lost 2-4" and there have been some pinwheels, but no avalanches.

Crystal Mountain Ski Patrol reported an avalanche cycle from precipitation Sunday night into Monday, with explosive and ski triggered storm and wind slab at higher elevations and some loose wet activity at mid-elevations. Also, two natural storm slabs were observed up to size D2 (large) on N-NW slopes in the 6000-6500 ft. range.  There were no new avalanches on Tuesday or Wednesday,

Both Mt. Baker pro-patrol and WSDOT avalanche professionals at Chinook Pass on Monday reported natural avalanche activity with storm slabs likely releasing during Sunday night's storm. 

Mt. Baker pro-patrol saw a very active day on Tuesday with numerous large glide avalanches releasing down to steep rock surfaces near and below 5000 feet in elevation.  Besides the glide avalanches, widespread natural loose wet activity ranging from small to large was observed on Shuskan Arm.   

 

Detailed Forecast for Thursday:

Thursday

A front crossing the Northwest Wednesday night and Thursday will bring renewed rain across the Cascades and Olympics followed by a modest cooling trend and a change to some snow at higher elevations. 

Poor and wet snow conditions are expected to continue Thursday.  Loose wet avalanches are still possible in steeper terrain. Larger and more dangerous wet slab avalanches or glide avalanches that release to ground over smooth rock bed surfaces are again possible on Thursday. Significant snowpack settling that has already occurred may reduce the problems in some areas, but in areas that have more recently warmed above freezing, there should be more wet loose, wet slab or glide activity, such as the Cascade Passes and in locations east of the Crest, with an elevated concern for the Northeast Cascades.

Friday Outlook

Moderate southwest flow should be seen on Friday, with a front approaching over the coastal waters. Moisture ahead of the front will bring moderate to heavy rain and snow to the Olympics and Northwest Cascades with much less precipitation elsewhere. Overall snow levels on Friday should be lower than Thursday.

The Olympics and Northwest Cascades on Friday should receive significant new snow. New wind and storm slab layers in the near and above treeline should be the main avalanche problems in these areas. 

Elsewhere, a lack of rain and snow and the 24 hours of cooler temperatures should mainly lead to consolidating snow, with refreezing at higher elevations.

Remember that closed ski areas without avalanche mitigation are equivalent to backcountry terrain!  Also, numerous early season non-avalanche hazards exist for backcountry travelers such as open creeks and barely buried rocks and trees.  

 

No Corresponding Mountain Weather Forecast Available