Boletín de aludes

Snoqualmie Pass

Northwest Avalanche Center
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Peligro de aludes

Tue
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Dangerous avalanche conditions will persist on Monday as Snoqualmie Pass receives another round of rain and snow mixed with wind. Make conservative decisions and avoid areas where avalanches can run or stop.

Problemas de aludes

  • Wet Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2

    The current snowpack above the 12/9 crust will continue to be of concern for Wet Slab avalanches on Monday. With continued loading Sunday night and Monday, water could percolate through the snowpack and pool on this crust, weakening the bonds between snow crystals to release large natural avalanches. The timing of wet avalanches is very difficult to predict and they can act in surprising ways, so minimize your exposure by choosing safe travel routes, staying off slopes over 35 degrees, and being aware of terrain above you at all times. 

    (12/20/2020) In the neighboring West South zone, the Crystal backcountry saw numerous D2 naturals on Saturday night which were 40-80 cm deep. When will Snoqualmie Pass reach its tipping point?

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2

    Above the rain/snow line, you should find significant new snowfall and dangerous Storm Slabs. The new snowfall combined with strong winds will thicken existing slabs sitting above the 12/9 crust. Avalanches could break within the new/wind loaded snow or involve all of the recent snowfall from this past week by breaking on weak snow grains a few inches above the 12/9 interface. Expect to find multiple interstorm layers capable of producing a failure within the snow above the 12/9 crust. Use small slopes and hand pits to gather information about which storm layers have the potential to fail and how they may react to your weight. 

    (12/18/2020) As of Saturday afternoon, there was roughly a meter of snow over the 12/9 crust at middle and upper elevations at Snoqualmie Pass. Avalanches would be large enough to bury and kill you if this slab is released.

Avalanche Discussion

After a relative break in the stormy conditions on Sunday, Snoqualmie Pass is set to continue its pattern of wet and wind on Sunday night and Monday. This time, instead of peak instability being found overnight, you could find that peak instability is during the day on Monday as temperatures warm and precipitation switches from snow to rain, producing a natural avalanche cycle. Wet avalanches are notoriously difficult to predict since they are not well understood, but avalanche danger often peaks during and shortly after periods of heavy precipitation. Wet loose avalanches should begin first as snow surfaces become wet and weak with the onset of rain. These avalanches are capable of entraining lots of snow and running far distances, even on low angled slopes. They can even trigger slabs as they descend. Wet Slabs often don’t occur until water is able to percolate into the snowpack and destabilize a weak layer. This can happen hours after the onset of precipitation, meaning the snowpack should still be capable of producing wet avalanches below the rain/snow line well after the rain has stopped. As you ascend in elevation above the rain/snow line, realize that your avalanche problem will be changing from wet to dry slabs and you will need to adjust your mindset. If you find that there are natural avalanches happening all around you, the danger is heightened and you should avoid all avalanche terrain. 

Prior to Saturday night’s rain event, the snowpack around Snoqualmie Pass contained up to 3 feet (a meter) of snow sitting on top of some weak snow crystals (12/13) which are just above a crust (12/9). So far, we have not confirmed any avalanches on these weak grains at Snoqualmie Pass. However, several avalanches occurred on this layer at nearby Stevens Pass and Saturday night produced a widespread natural cycle in areas of the neighboring West South zone. We are lacking observations from Sunday for the Snoqualmie Pass zone, but Alpental patrol reported a few natural slabs releasing within the ski resort on Saturday night. We are uncertain if the widespread avalanche cycle we are expecting has happened at this point, so we treading carefully and wondering if the additional load from this storm could be all that is needed to tip the scales and produce larger, more devastating avalanches. We are not out of the woods yet as there are plenty of slopes that haven’t slid which we expect should at some point. 

Below the rain/snow line, heavy snow and challenging travel conditions will be found. Anticipate open creeks, thin coverage, and plenty of obstacles to navigate. 

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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