Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

On Sunday, you may be able to trigger avalanches in the recent snow on a variety of steep slopes. Avalanches will be bigger and more dangerous near and above treeline where you find freshly drifted slabs of snow. Avoid steep open slopes with stiff wind-drifted snow and seek out lower-angle or sheltered terrain.

Problemi valanghivi

  • Wind Slabs

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

    Expect more east winds transporting snow on Sunday. Avalanches will be bigger and easier to trigger above treeline where you find freshly drifted snow. You may find older wind features from west winds. Watch for patterns of drifting and any actively blowing snow to point out the leeward, loaded slopes. Use caution near and below cornices. They've grown large and can fall without warning.The most likely places to trigger wind slabs will be steep slopes below ridges, steep convex rolls, and the base of cliffs. Feel for stiff over soft snow layering and look for signs of cracking to identify areas of unstable, wind-drifted snow. Avoid slopes over 35 degrees if you find the new snow sliding easily or test slopes producing mini avalanches.

    (3/3/2023)

    In specific places like wind lips on ridge lines we could trigger small wind slab avalanches. Upper Twisp River drainage

    Photo: Willie Webster

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    In many sheltered areas, you can trigger small avalanches on steep slopes. Loose, uncohesive snow could slide below your feet or machine. While these avalanches often are easier to avoid once triggered, they can be dangerous at times. Be especially cautious in very steep terrain near rocks, cliffs, tight gullies, and other terrain traps. If loose avalanches run particularly fast or are forcefully, take care to stay out of them and not be below the moving snow.

    (3/3/2023)

    A triggered dry loose avalanche.  Upper Twisp River drainage

    Photo: Willie Webster

Avalanche Discussion

Observers reported 2-3 large (size D2) natural slab avalanches on northeast aspects of the Hairpin valley near Washington Pass. These likely occurred on Friday. Also on Friday, NWAC observer Willie Webster found about 8" of new snow near the head of the Twisp River drainage.  He was able to trigger small loose avalanches in the surface snow along with some isolated areas of cracking and freshly wind-drifted snow. Below 6,000ft there was little to no cohesion in the new snow.

On Wednesday, Willie identified weak snow below the Valentine's Crust near Washington Pass. The weak snow adjacent to the crust was reactive in snowpack tests, and he experienced some isolated collapses on this layer. He noted the instability seemed isolated to the 4000-5000ft elevation band. This crust can be found up to 7,000ft in the zone and varies with elevation and proximity to the crest. While we have not seen any avalanche activity on this layer, we are closely monitoring this interface. Near Washington Pass, the Valentine's crust is 2-2.5 feet below the surface. The January 5th surface hoar can still be found over 3 feet below the surface on many slopes. You may be able to identify the layer as a grey stripe or with planar results in snowpack tests. The layer isn't currently a concern for avalanches.

Last week, large cornices fell intermittently. The additional wind and snow should keep cornice falls on your mind. They are a hazard on their own but also could trigger an avalanche if they land on steep slopes below. Best to give these hazards wide margins as you travel. 

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