Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
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

Recent snow fell on weak, variable surfaces, and triggering large and dangerous avalanches is likely. Avoid steep terrain in both sheltered, steep, shady aspects and steep wind-drifted slopes. Pay attention to red flag signs of instability, such as collapsing.  Keep your terrain choices simple and slope angles low. 

Problemi valanghivi

  • Wind Slabs

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

    Wind slabs formed from the recent snow and winds may rest over weak or slick snow surfaces and could remain sensitive for longer than usual. They could step down to deeper weak layers, and break wider than anticipated.  Avoid steep slopes below ridgelines, the base of cliffs, and cross-loaded terrain features. Textured surfaces and visible blowing snow are great visual clues to identify wind-affected terrain. Cracks shooting out from your equipment are another key sign that these wind slabs are unstable. With the recent high wind speeds, slabs might be hard and break above you or have formed further down the slope than anticipated.

    On southern aspects or sheltered slopes, you may also see small storm slab avalanches or fast moving dry loose avalanches. 

    (2/16/2022)

    Small wind drifts would crack and release easily off ridgetops on Wednesday. Shortly below the ridge we didn't find any wind affected snow.

    Photo: Nate Hough-Snee

  • Persistent Slabs

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

    The current snowpack is tricky, variable, and dangerous. Triggering a large or surprising avalanche on persistent weak layers in the snowpack is possible. The distribution of this problem is hard to isolate, but we expect it to be most likely in shaded, northerly terrain. Consider avoiding steep terrain on this north side of the compass, especially in sheltered areas like open glades within the forest. If you hear and feel whumping collapses, these are a bullseye sign of unstable snow, and you should stick to low-angle terrain.

    Many areas don't have much of a cohesive slab over these persistent weak layers, and the layer itself is quite variable throughout the terrain. This makes it a tricky problem to pin down, with a high likelihood of getting surprised by finding that one spot where you could trigger an avalanche. Two adjacent slopes might have very different stability. The safest terrain management option for this problem is avoiding it altogether by staying on low-angle terrain or moving to southern aspects. 

    (1/19/2023)

    An example of a persistent slab in gladed terrain, like you might be able to trigger.

    Photo: Ryan Minton

Avalanche Discussion

1-2ft of recent snow fell on widely varying surfaces. Stevens Pass Ski Patrol and WSDOT avalanche forecasters reported mostly small storm slab avalanches, with a few larger wind slabs, releasing on the old surface or within the new storm snow. The new snow lacked cohesion due to the cold temperatures, and some backcountry users reported more dry loose avalanches than slabs. Another observer reported propagating extended column test on a layer of faceted snow and observers throughout the zone reported widespread collapsing. Overall, the results are mixed, but we're concerned with lingering instabilities on the January Drought Layer (JDL) on these northerly aspects. 

I was out in the Henry Creek Area today to check on the state of our weak snowpack. Traveling through the low-angle clearcuts, we experienced numerous collapses. I found two layers of concern in snow profiles. The deepest layer is buried 20-23in down and consists of 1-2mm faceted grains over the 1/10 crust. Above that, buried 15-20in, is the surface of the January Drought Layer, which is 1cm buried surface hoar over another layer of 1-2mm faceted grains. I also observed a deep crown on a steep southern aspect at 5700ft, adding to our uncertainty. 

You can help us build that data set by submitting an observation HERE or via the Avy App. 

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