Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

A relatively warm and somewhat complex storm will bring snow and rain to the area overnight and into Monday. It may be easy to trigger avalanches in the new snow and they could occur naturally. Give yourself plenty of safer terrain options, and be ready to stick to lower-angle slopes if conditions are more dangerous than anticipated.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    A relatively warm storm may create hard over soft layering in the upper snowpack, setting the scene for dangerous conditions. Watch for natural avalanches, cracking in the snow, and small test slopes that slide easily as indicators of instability. If you see these "red flag" signs, stick to well-supported slopes under 35 degrees. Use quick tests frequently as you travel to assess the conditions. If you find more than a foot of new snow, avalanche conditions could be even more dangerous than forecast.

    Above treeline, avalanches could be bigger and more dangerous. Avoid steep leeward, wind-loaded slopes. Pay close attention to blowing snow and any recent wind drifting patterns.  Be aware that cornices have gotten quite large and have occasionally fallen during recent storm and loading events. Stay out from under terrain with large, looming cornices and err on the conservative side if visibility is poor and you can't see the overhead slopes.

    (3/5/2023)

    A skier-triggered avalanche from last week. S, 5,600, Upper Twisp River

    Photo: Willie Webster

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    Loose avalanches will be possible where the snow surface becomes moist from rain, wet snow, or sun. There's a chance for some breaks in the clouds in the afternoon. You'll want to exercise caution near terrain traps like above cliff bands or tight gullies where a slide could push you into hazards. Sticky, moist surfaces and wet snow that slides easily are good indicators that you could trigger an avalanche. 

    (11/25/2022)

    An example of small loose avalanches above Highway 20 from earlier this seaon.

    Photo: Willie Webster

Avalanche Discussion

On Sunday, a brief storm brought high snowfall rates and light snow totals to the eastern half of the zone. Observers reported several inches east of the Silverstar drainage and less snow further west. Observers reported a handful of avalanches in the past couple of days with natural loose dry avalanches to size D1.5 on Saturday. On Friday, large (D2) wind slabs ran on north, west, and southwest aspects around the Hairpin Valley. Some of these had crowns up to 4 feet deep, where snow sifted off of cliffs to form deeper slabs. 

On Friday, Drew Lovell reported from a prolonged period near Hart's Pass, where his concerns lay in the recent snow and alternated between loose and wind slab avalanches.  Also on Friday, Wille Webster was in the Silverstar area and found up to 3 feet of recent snow since late February. An observer on Wednesday reported a thin sun crust (likely formed Sunday) below the recent snow on southerly slopes, the crust faded away at higher elevations.  Significant snowfall and intermittent wind events since late February have brought loose avalanches or the occasional small wind or storm slab avalanche. In that time, the snowpack has gained close to 3 feet in many locations.

The Valentine's crust is 3-5 feet below the surface in the western half of the zone, including near Washington Pass, the upper Silverstar drainage, and Hart's Pass. You can expect to find it closer to the surface at lower elevations and further east in the zone. There have been numerous observations and snowpack tests indicating weak snow and poor structure below the crust. While avalanches on this layer seem unlikely, there's a chance that the weight of the new snow could initiate a slide in places where the crust is crumbly and breakable. If you're motivated to dig deep enough, you can probably still find the January 5th surface hoar. It's so deep and rounded, that it hasn't been a concern for avalanches in over a month near Washington Pass. We have less of an understanding of the progression of these layers east of Mazama and the Twisp River drainage.  

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