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

Issued: 9:11 PM PST Wednesday, February 7, 2018
by Kenny Kramer

Strong winds will move any loose snow at higher elevations on Thursday, whether it is falling from the sky or scraped from the old snow surface. Avoid steep, wind-loaded slopes where you observe signs of active snow transport.

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Avalanche Problems for Thursday

Wind Slabi

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Forecast for Thursday:

A cold front will usher in cooler weather and strong W-SW winds to the east slopes of the Cascades on Thursday with limited moisture from the frontal system spilling over to the east slopes. What limited snow does spill over will generally be near the Cascade crest in the above treeline terrain.

Watch for small to large wind slabs developing mostly above treeline, but in some cases extending into the near treeline terrain. The new snow may or may not bond well to the old snow surfaces, but even small amounts of new snow will quickly form slab given the strength of the winds on Thursday. If recent winds and warm temperatures have left any recent snow available for transport in the above treeline zone, expect that winds will also deposit that snow on leeward snow. If you see snow being transported on Thursday, avoid leeward slopes. 

With cooling temperatures, winds, and limited recent snowfall, it is likely that loose wet activity will not be an issue on Thursday. 

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.

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 Wednesday. Up to 8" of wind-hammered or sun/rain moistened snow now sits and is well bonded to a crust formed by a rain event on February 4th 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, trending the hazard from stubborn toward unreactive on Tuesday. With the recent warm temperatures, these slabs should be generally unreactive to trigger.

A natural avalanche cycle has been reported in many areas from Monday’s (1/29) warm and wet weather with some of these avlanches triggered by cornice fall. 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 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 is 8" of snow available for wind transport. Also of note, the party witnessed evidence of produced a very large avalanche (D2.5) in Spire Gulley, which was likely produce by cornice fall triggering a wind slab, which then entrained a lot of 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'.

On Sunday, snow professionals at the Barron Yurt near Hart's Pass reported stormy conditions with denser snowfall increasing the likelihood for storm slabs during the day due to rising temperatures in and around the 6000' level. Moderate winds were continuing to transport snow onto lee slopes near and above treeline. No deeper instabilities were noted in snowpack tests. Observations were limited in this terrain due to poor visibility. On Sunday in terrain further to the east, a wet loose cycle was noted below 6000'. 

On Saturday, snow professionals at the Barron Yurt near Hart's Pass reported about 6" of new snowfall over the preceding 24 hours. 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. 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
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.