Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

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Limite del bosco
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The avalanche problems you experience Friday will depend on your exposure to the sun. On more southerly slopes, watch for small natural loose avalanches that may run far on a frim crust. In shadier terrain, keep your eyes peeled for subtle clues that the wind formed soft slabs within the recent snow.

Problemi valanghivi

  • Loose Wet

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

    Sunshine and warmer temperatures should cause the snow to shed from steep southerly slopes Friday. When you notice the snow falling out of the trees or observe new rollerballs start to anticipate natural loose avalanches. While the modest amount of soft snow on the surface should limit the size of these slides, they may run farther than you anticipate due to an underlying crust. Be leery of any steep slope receiving direct sunshine, especially where a small avalanche could push you over a cliff or into a creek. If the sky becomes cloudier than forecasted, this avalanche problem may not materialize, and you could see locally lower hazard.

    (12/2/2020) Example of rollerballs on a steep rocky slope.

  • Wind Slabs

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

    Weather stations and on the ground observations confirmed strong E-SE winds this week with blowing and drifting snow. We received one report of a small skier triggered avalanche on a cross-loaded feature near Gem Lake. However, many travelers did not observe wind slabs in the terrain. This avalanche problem may be confined to features more exposed to SE winds and could hide under a few inches of a softer surface. If you travel on SW-N-NE aspects keep a sharp lookout for any signs of wind-affected snow. Drifts behind objects and even a subtle change in the feel of the snow underneath you may be your only clues of wind loading. Even small wind slabs can harm you in high consequence terrain. 

    Wind slabs remain in the forecast because these are the locations where a significant slab may overlay weak older snow grains buried this past weekend. If an avalanche fails on these persistent grains it could trigger easily, propagate widely, and run quickly. As a result, these may not be your normal Snoqualmie Pass wind slabs and could deserve a more cautious approach.

    (12/22/2020) Example: a small wind slab in a confined terrain feature. You may see similar slides in terrain exposed to the SE winds.

Avalanche Discussion

You should find 6-10” of soft dry snow over the prominent and firmer 1/13 crust layer around the Pass. This is a result of several small incremental storms over the past week. As a result, subtle layers and thin crusts may occur within this thin upper snowpack. On Saturday (1/23) facets, surface hoar, and a thin sun crust were all observed throughout the zone and subsequently buried that night. So far, no avalanches have occurred on these persistent weak grains, but some travelers observed cracking and collapsing above 4500’ in shaded terrain. As temperatures warm, this could change how this layer reacts to a trigger. 

While the recent snow greatly improved travel conditions across the zone, you may still encounter icy slopes under thick tree cover. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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