Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Update 7:30am January 11: Slab avalanches remain possible even below treeline and well outside of wind affected areas. Expect a fairly calm day on Wednesday before a strong winter storm arrives and increases avalanche danger markedly. Continue to look for signs of instability like shooting cracks in the wind zone, and be suspicious of steep, sheltered, sparsely treed slopes. Steer around steep, consequential slopes if you find instabilities or stiff slabs over weaker snow at any elevation.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2

    You could find wind slabs of various thicknesses on a variety of higher elevation, exposed slopes. Winds have shifted between easterly and westerly directions, so you could find reactive slabs on all aspects.Look for textured surfaces as you gain elevation. Other clues to wind slab are drum-like, firm snow over softer snow. Look for signs of instability like shooting cracks in wind drited snow, and use small test slopes to check how these areas may react. You can stick to wind scoured ridgelines, or lower angled slopes to avoid this problem. 

    (1/5/2023)

    A triggered small (D1) avalanche on the leeward side of a ridge in Liberty Bowl, next to South Early Winter Spire. SW, 7,450ft.

    Photo: NWAC Public obs

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2

    Outside of wind affected areas, some potential for triggering slabs on buried surface hoar, or a slick crust from Christmas does exist. Persistent slabs have become a problem in the adjacent East Central zone, so they could be an issue in some areas of the East North. A skier triggered a large slab at 4,800ft near Silverstar on Tuesday, and we should take this as bullseye evidence. Look for long shooting cracks as you travel, and check for planar failures with a variety of tests. Sparsely treed, sheltered terrain that faces north and east may be the most likely areas to find this instability. 

Avalanche Discussion

Wednesday should be a fairly calm day before the storm. Expect increasing winds later in the day, and increasing avalanche danger overnight into Thursday as a major storm arrives.

On Monday, Willie reported two small soft slab avalanches hit the closed Hwy 20 in the Liberty Bell group on Monday morning. Winds were strong with intense blowing snow in the morning, then skies broke and the wind calmed down. Shallow storm slabs were easily triggered about 8" down. Tests showed potential for failure down about 1ft and 1.5ft on large, preserved stellars.

Last weekend was an active one in the eastern Cascades. On Sunday, a party reported triggering a small slab near Varden Creek on a north aspect at 6,000ft. The skier that triggered the slide was the fourth on the slope, and got carried a little ways but was luckily ok.  WSDOT forecasters reported a wet avalanche that gouged to the ground near the town of Methow. On Saturday, an observer near Twisp reported a mix of snow and rain with a similar avalanche gouging to the ground. Another observer near Washington Pass reported cracking near treeline. 

A cycle of very large avalanches occurred December 24-27th near Washingotn Pass involving older weak layers that were buried in late November and early December. Near the pass, the weak layers are now capped with a stout crust and melt-forms from the Christmas rain event.

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