Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous conditions are expected at upper elevations, where avalanches may be larger with thick slabs from the recent drifting. Outside of wind exposed areas, riding conditions should be excellent but the new snow may still slide easily on a recently buried layer of surface hoar and crusts.  Consider using lower angled and well supported slopes away from larger terrain features.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    Winds were blowing strong from the west on Sunday. As temperatures cool of, the winds should taper a bit, so wind slabs may become hidden by newer soft snow. Even still, expect to find thicker and stiffer slabs on high, exposed slopes. Slabs may be resting on a layer of faceted grains, surface hoar and crusts. 

    Because of the nature of these weak layers, avalanches may fracture widely across terrain features and in some cases, could be triggered from adjacent slopes. The most likely place to trigger one of these would be beneath heavily loaded ridgelines and below large cliff outcroppings. You can stick to lower angle and sheltered slopes to steer away from the problem.

    Example large natural slab avalanche from last year.

    Photo: Willie Webster

  • Storm Slabs

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

    The new snow is stacking up quickly. Storm slabs should be most reactive in the morning, and instability may linger through the day. Slabs could break within the new snow, at the old snow interface, or potentially even deeper on a crust from late January. The new snow recently buried a layer of facets and surface hoar on sheltered slopes, even on southerly aspects. If you find one of these areas, slides may fracture widely or be triggered from adjacent slopes. Loose snow slides may run fast and far on Monday. Look for fan shaped avalanches to clue you into these.

    You can look for signs of instability like shooting cracks, and listen for whumphing collapses. Stick to lower angled and simple terrain, away from larger terrain features for the time being. 

Avalanche Discussion

Winds were cranking from the west on Sunday, and the front brought a few hours of heavier snowfall to the mountains. You're likely to find at least 6-10" of new snow at mid elevations. As the temperatures drop, winds should lessen. This is good for riding quality, but with a tricky snowpack it'll be a good day to give larger terrain features at upper elevations some respect.

Prior to the front on Sunday, observers had been finding weak surfaces including surface hoar and facets, sometimes overlying a thin sun crust. The wind may've helped knock down some surface hoar and break up some facets, but we should assume much of it was buried intact. 

On shady slopes, at mid and upper elevations, there is up to 1.5ft of recent snow over a stout crust from January 31st. Observers have found a thin layer of weak facets just above the 1/31 (elsewhere early February) crust. In the East Central zone, backcountry travelers have triggered a number of avalanches just above the crust, with the most recent being on the 22nd. With a stormy week ahead, we'll be watching the weak layer as a potential culprit for avalanches. Lower elevations hold substantially less new snow over this crust and often don't harbor the associated facets. 

Snowpack information is limited outside of the Highway 20 corridor and Harts Pass. Let us know what you find if you get out into the backcountry!

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