Boletín de aludes

West Slopes Central

Northwest Avalanche Center
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Peligro de aludes

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

Lo esencial

A transition from snowfall to rain will trigger a round of natural avalanches. Most of these should occur overnight but could continue into the morning hours if heavy rain persists. Avoid being on or under steep terrain holding wet snow

Problemas de aludes

  • Wet Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    Wet avalanches of all varieties are in the forecast for tomorrow. The peak of natural avalanche activity should come overnight, especially when snowfall transitions to rain. But light rainfall and warm temperatures are forecast to continue for most of the day and keep elevated the danger from wet avalanches. If snow levels are higher than anticipated, we’ll see wet avalanches work their way into upper elevations.

    There isn’t really much you can do to avoid these other than stay out of the way, especially when it's raining. Don’t linger under big, steep terrain, and also be wary of gullies a bit lower down that can funnel avalanche debris from higher up. Small wet avalanches from cliffs and other steep terrain overhead can still do plenty of damage or push you into terrain traps below.

    (12/5/2023)

    A recent natural wet avalanche ran to the ground and entrained dirt adjacent to Skyline Lake (Stevens Pass). 5,100ft, SSE

    Photo: Josh Hirshberg

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    No changeover to rain is expected at upper elevations so new snow should pile up into dense slabs. Heavier, denser snow will load up over lighter, drier layers below. Fresh slabs could be stubborn to trigger but quite large. Lower-than-forecast snow levels could help dry snow - and unstable slabs - hold on at mid-elevations as well. 

    If you make it up to dry snow on Sunday try to use small slopes and hand pits to assess the bond of new snow layers. The strong over weak interface you are looking for might be deep enough that you would need to pull a shovel out of your pack and dig a pit to assess. On the other hand, shooting cracks or whumphing should be all the information you need to avoid steep terrain. Maybe best to give steep upper-elevation slopes another day to recover from the storm.

     

    (12/13/2022)

    Example of a natural  slab avalanche on at upper elevations

    Photo: NWAC Public Obs

Avalanche Discussion

The forecast for Sunday isn’t too tricky, but avalanche danger will hinge on a variety of factors including how much it snows, how much it rains, and most importantly, when does snow transition to rain. In West Central the bulk of the precipitation, warming, and natural avalanche activity should occur in the middle of the night. But first look for proof natural avalanche activity is on the decline before you assume it is. 

Also,  weather and avalanche conditions could vary widely across short distances. If you are traveling in a portion of West Central near Stevens Pass or Snoqualmie Pass then read the forecasts for those zones.

If you are out in the mountains start in simple terrain with no overhead exposure until you get a handle on conditions. Some questions would be:

  • Are you observing active signs of instability or natural avalanche activity?
  • What is the size and extent of recent natural avalanche activity? 
  • How hard is it (still) raining?
  • Is there dry snow as you gain elevation? And how much?
  • Is your plan for the day going to work given avalanche, snowpack, and weather factors?

Another day has passed with no observations from West Central. Very strong winds raged in West North with a gust of 64mph recorded at Pan Dome at the Mount Baker Ski Area. Fresh snowfall was also recorded at Heather Meadows (10” by 4:00 pm) but it was hard to say how much actually fell due to high wind speeds alternately drifting and scouring snow in normally sheltered terrain.

Intense wind transport and slab formation were the themes for the day with a few human-triggered avalanches reported. All were small in size and occurred in freshly wind-loaded terrain. One was remotely triggered from a short distance away. Less wind and no fresh avalanches were reported form Stevens or Snoqualmie Passes.

 

 

 

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