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East Slopes Central - Lake Chelan to South of I-90

Issued: 8:11 PM PST Saturday, February 3, 2018
by Josh Hirshberg

Stormy conditions and a rising snowline will increase the avalanche danger on Sunday. Fresh wind slabs will be increasing in size and sensitivity above treeline. Loose wet avalanches will become more likely to trigger in areas and elevations that see a switch from snow to rain Sunday. Avoid slopes where small avalanches may have large consequences such as above cliffs, rocks, creeks, and gullies.

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Avalanche Problems for Sunday

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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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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Forecast for Sunday:

Light to occasionally moderate precipitation near the Cascade crest, increasing crest level west winds, and a rising snow line will increase the avalanche danger on Sunday at all elevations. 

Loose wet avalanches will become more likely to trigger in areas and elevations that see a switch from snow to rain Sunday. You will be able to trigger loose wet avalanches on steeper slopes during and immediately following rain events. Avoid slopes where small avalanches may have large consequences such as above cliffs, rocks, creeks, and gullies.

Moderate to strong winds will continue to form fresh wind slabs on a variety of aspects above treeline. Fresh cornices, snow drifts, plumes, and blowing snow all indicate where wind slabs are forming. Fresh wind slabs will be increasing in size and sensitivity Sunday.

Large cornices exists along ridgelines. Warming temperatures and rain will make these massive blocks of snow more likely to fail. It is very difficult to predict when and where cornices will fall. Avoid traveling on or below cornices.

The avalanche hazard will be lower in areas receiving less precipitation further east of the crest.

Avalanche Summary:

Moderate to strong westerly winds at crest level mixed warm temperatures down to valley floor along the east slopes of the Cascades on Saturday, with valley or lower elevation sites such as Lake Wentachee, Tumwater and Mazama popping up to near or above 50 degrees. The freezing level hovered around 5500 feet in the northeast Cascades, increasing to 6000-7000 feet further south and east. Light precipitation noted near the Cascade crest quickly diminished further east. Wet snow conditions were noted near and below treeline along the Hwy 20 corridor. Continued snowpack settlement was also noted in these elevation bands at NWAC and Snotel sites. 

8" of new snow was reported in the Washington Pass area Friday while for areas south of Holden, rain fell up to about 6000 feet. Very touchy wind slabs formed and developed in the Washington Pass area Friday and again Saturday near and especially above treeline.

A natural avalanche cycle has been reported in many areas from Monday’s (1/29) warm and wet weather. Rain occurred along the east slopes as far north as Holden, 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

On Saturday, a professional in the Washington Pass area reported about 6" of new snowfall over the preceding 24 hours. Very touchy wind slabs were present near and especially above treeline with moderate to strong W-SW winds transporting new and recent snow onto lee slopes. Storm slabs were generally unlikely to trigger. Moist surface snow conditions were present below 5800'. The 1/16 crust was 4 to 5 feet down. Similar conditions were reported Friday in this area. 

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

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.