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East Slopes North - Canadian Border to Lake Chelan

Issued: 6:26 PM PST Thursday, February 8, 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. 

Moderate to strong crest level winds continue to move shallow recent snow at higher elevations. Variable shallow wind slabs are likely on a variety of aspects Friday. Avoid steep, wind-loaded slopes or features where you observe signs of active snow transport.

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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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Avalanche Summary:

This has been a long and windy period for the east slopes of the Cascades where gusty westerly winds blew snow around from Sunday night through Thursday. Generally 3-6 inches of new snow overlie the most recent melt-freeze crust near and above treeline. The crust formed up to 5800-6800 feet in the northeast Cascades, extending to slightly higher elevations further south. Significantly less snow sits on the crust further east of the crest and also to the south, decreasing wind slab potential in these areas.

Wind slabs were identified throughout the near and above treeline terrain, but they were pretty stiff and well bonded in the alpine, making triggering an avalanche more difficult. 

A natural avalanche cycle has been reported in many areas from Monday’s (1/29) warm and wet weather with some of these avalanches triggered by cornice fall. Rain occurred along the east slopes as far north as Holden Village, WA.

Scattered observations from the last week of January found buried surface hoar on top of the 1/16 crust. This persistent weak layer was found or thought to be the cause of several avalanches. Extra caution should be taken when traveling in areas further east of the crest where this layer may survive. Snow profiles and snowpack tests are the only means to identify and locate this layer.

Observations

North

Wednesday, Avalanche professionals in the Washington Pass area traveled to near treeline, finding about 4 inches of new snow over a 1 inch crust at about 6000 ft. Less new snow was below treeline with shallow wet snow below the rain line about 4500 ft.   Strong crest level winds were transporting snow, but due to the gusty nature, uniformed wind slabs were not observed and no avalanches were triggered in steep wind affected terrain.  

On Tuesday, snow professionals in the Washington Pass area reported lots of wind-effected snow, which was pretty stiff, but well-bonded, producing very resistant results in shear tests. Closer to the Cascade crest there was 8" of snow available for wind transport. Also of note, the party witnessed evidence of a very large slab avalanche (D2.5) in Spire Gulley, which was likely triggered by cornice fall, entraining  significant loose and wet snow during the slide cycle on Sunday. 

On Monday, snow professionals in the Washington Pass area reported a recent maximum rain/snow line of 6,800 ft. Subsequent snowfall prevented much refreezing of the wet snow. Winds were unusually gusty and variable with no dominant wind direction and some wind slab was present into the below treeline zone. The party triggered a small wind slab quite low in the terrain. They messaged a high level of uncertainty regarding reactivity and location of wind slabs in this zone. Glide activity was also evident to 6000'.

 

Central

An avalanche professional traveling in Icicle Creek Thursday found 6-8” of settled snow well bonded to the 1/29 crust. Observations demonstrated a strong upper snowpack. No buried surface hoar was found in this location.

On Tuesday, Mission Ridge Pro Patrol identified several layers of concern in this regionally shallower snowpack. These layers should be watched during future loading events. Similar basal weak layers were found in the nearby shallow snowpack of Blewett Pass.

South

No recent observations

Forecast for Friday:

Significant cooling is expected Thursday night through Friday with little to no additional precipitation. This should allow previous moist to wet surface snow to re-freeze and form a strengthening crust below treeline. The cooler temperatures Friday should limit any wet snow avalanches.

Winds should taper Friday but cold temperatures should help preserve any recently formed shallow wind slabs at higher elevations. Watch for shallow wind slabs mostly above treeline, but in some cases possible in near treeline terrain. If you see snow being transported on Friday, avoid leeward slopes. 

Large cornices exist along ridgelines and have been sagging recently due to warming. Give cornices a wide birth and limit your exposure as much as possible if you must travel under them. Cornice fall is unpredictable.

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.