Boletín de aludes

West Slopes North

Northwest Avalanche Center
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Peligro de aludes

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

Lo esencial

Natural avalanche activity should wind down in the morning but large natural avalanches are still possible. Give big steep slopes plenty of room while temperatures cool, precipitation becomes lighter and the new snow stabilizes.

Update @ 7:05am:  Danger raised to High due to heavy precipitation extending through the morning hours. Avoid all avalanche terrain including runouts and gullies below big avalanche paths. Danger will decrease as rain and snowfall  amounts become lighter.

Problemas de aludes

  • Storm Slabs

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

    Above the rain-snow line, there will be plenty of new snow, especially in alpine terrain. The likelihood of seeing a natural slab avalanche will decrease but conditions will still be quite dangerous to start the day. 

    You might find shallow slabs that are reactive to the weight of a single person on steep slopes. These could even build through the day with light snowfall and wind speeds strong enough for snow transport. The bigger concern is thick slabs of dense new snow. They are often difficult for a person to trigger but produce destructive avalanches when provoked by a smaller loose snow avalanche, falling cornice, or some other sizeable trigger. 

    The best bet will be to just avoid traveling on or under big, steep slopes. Smaller bites of avalanche terrain might be reasonable in the second half of the day as the new snow stabilizes with a cooling trend. The usual tests for assessing new snow stability (test slopes, etc.) will be useful to get a read on shallower slabs found in the upper layers of new snow. The same tests don’t say much about the bond of a thick new snow layer to the old surface below.

    Large slab avalanche triggered by cornice fall during a rain event in the spring of 2022. Rain rills are visible on the snow surface lower on the slope.

    Photo: Julz Holder - Grounding Truth

  • Loose Wet

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

    While the bulk of the wet avalanche activity should occur overnight, danger from cornice falls, wet loose, glide and wet slab avalanches will persist. Friday won’t be the kind of day where you will be looking for rollerballs and other signs of instability to figure out when to move away from steep terrain. All the signs should be there in the morning - it’s just a matter of staying out of the way. Avoid traveling below glide cracks, sagging cornices, and other terrain features that routinely produce wet avalanches.

    Example of wet loose avalanche activity from a rain event in 2019.

Avalanche Discussion

The approaching storm ended up moving in a bit behind schedule Thursday. A mix of rain and snow dribbled in through the afternoon and the first precipitation measurement with greater than 0.10”/hr didn’t occur until 5:00 pm at the Heather Meadows weather station. Other weather stations around the zone showed temperatures in the upper 30s, but temperature alone was probably not enough to have a significant effect. The expectation of seeing the beginnings of a natural avalanche cycle late in the afternoon just didn’t line up with reality.

Water amounts overnight - 1.5” of precipitation as snow above 5000’ and rain below - are still on track to have an strong effect on the not-very spring-like snowpack found across most of the Cascades. The heaviest precipitation should end by morning and be accompanied by a drop in snow levels. But it turns out mountain storms don’t read weather forecasts - be ready to change plans and expect higher danger if heavy rain or snowfall, or strong winds persist into the afternoon.

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