Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Wind Slabs may develop by the end of the day and be reactive to human triggers. Look for larger piles of windblown snow to steer around as you ascend in elevation, potentially on features where you’re not used to seeing them.

Problemi valanghivi

  • Wind Slabs

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

    On Tuesday, winds should be increasing throughout the day and changing direction, possibly creating Wind Slabs. Only a trace of new snow should fall from the sky on Monday night, but low-density snow from the past few days will be available for the wind to transport. Wind Slabs will be most likely near ridgelines on leeward slopes, but we often find unusual loading patterns at the pass during east wind events. So keep an eye out for textured snow surfaces, freshly building cornices, or active wind transport to let you know where the snow is being distributed. Those unusual loading patterns sometimes result in cross-loaded gullies or midslope pockets. Slabs should be larger and possibly more reactive as you ascend in elevation and toward the end of the day as wind speed increases. You could find that in isolated areas, slabs over a foot have been formed, while other areas may contain shallow slabs only a few inches deep. Avoid terrain features where you notice pillow-like piles of snow or the snow is no longer light and fluffy.

    (12/28/2020) An example of a human triggered Wind Slab on a north-facing convexity.

Avalanche Discussion

We have added a few inches of snow per day for the past few days at Snoqualmie Pass, increasing the depth of snow over the 1/13 crust. In terms of avalanche hazard, we continue to consider the 1/13 our “new ground” and are only concerned about instability above this layer. Sitting above this firm crust, we have new snow, multiple types of buried weak snow, and smaller crusts. Despite weak snow sitting atop a firm crust, we have not had many avalanche concerns lately because there hasn’t been enough depth or a slab. With the addition of strong winds to the zone by the end of the day on Tuesday, Wind Slabs could form over this weak snow. These potential slabs would provide us the element that has been missing recently to create avalanches and increase the hazard. 

The other hazard we have talked about a lot recently has been difficult travel conditions with firm surfaces, frozen avalanche debris, and breakable crusts throughout the zone. As we continue to add more snow on top of these old surfaces, travel conditions have started to improve. With strong winds set to impact the zone, some areas may be stripped of recent light snow back down to these hazardous surfaces. In other areas, avalanches could run on the buried firm surfaces, removing the recent snow. Regardless, you need to continue to prepare for possibly firm and challenging travel conditions until we get a bit more snow.

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.

Regioni coperte