Boletín de aludes

Banner Summit

Sawtooth Avalanche Center
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Peligro de aludes

Sun
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
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

Avalanche conditions will become increasingly hazardous throughout the day. This morning, your primary concern will be avalanches failing on weak layers buried 1-2 feet deep. These types of slides can be triggered from a distance away from the slope that avalanches. As the day heats up, the likelihood natural and human-triggered wet snow avalanches will increase significantly. If you're finding a thick pile of wet, mushy snow at the surface, conditions have become dangerous and you should consider avoiding avalanche terrain. 

Problemas de aludes

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–1.5

    Wet snow problems will develop with today's heat and sunshine. The snowpack was able to weakly freeze last night, but it won't take long for the crust on top to break down. You'll be most likely to encounter natural and human-triggered wet loose avalanches on steep slopes receiving direct sunshine. Avalanches will also become problematic on steep, shaded slopes at lower and middle elevations as the day heats up. These slides start out small and pick up speed and material as they travel downslope. In favorable terrain (long, steep, and rocky slopes) these avalanches may become large enough to bury you today. 

    If you're finding a thick pile of wet, mushy snow at the surface it is a good time to find a colder slope to play on or to head for home. Cascades of roller balls (wet balls of snow traveling downslope) are a good indicator that the snow is becoming wet. Conditions will deteriorate throughout the day, make sure to have a safe exit route in mind when things start melting down. 

    Read the Forecast Discussion below for more information about today's changing conditions. 

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–2.5

    Layers of weak snow buried underneath 1-2.5' thick slabs can produce large avalanches. The most recent triggered avalanche on these weak layers occurred on Wednesday when riders remotely triggered an impressive slide from 50 yards away (photo at right/above). The slide broke over 1,000' wide and 2' deep (more details here). I triggered a similarly large slide on Sunday north of Banner Summit (video here). Most of the avalanches that we've observed on these layers have failed on crust + facet combinations.

    Avalanches that fail on these weak layers will be large and destructive and will behave in surprising ways. Slides can be triggered from a distance away from steeper slopes. Several skiers or riders might traverse a slope before it avalanches—tracks on a slope are not an indication of stability. You can reduce your risk by staying off (and out from beneath) slopes steeper than about 35 degrees.

    ADDITIONAL DISCUSSION: Older weak layers lay buried underneath very dense, 3-5' thick slabs. Triggering a very large avalanche involving these weak layers has become unlikely, but unlikely and impossible are very different things. The most recent triggered avalanche involving these older weak layers happened last Friday, when riders triggered a very large slide from over 500' away (photo and details here). Smaller triggered avalanches, natural wet snow avalanches, and failing cornices can all be effective triggers for these beasts. Being caught in one of these slides would likely be unsurvivable. 

    (4/5/2023) This avalanche was remotely triggered by two snowmobilers from a meadow 50 yds to the side of the slope. The slide broke over 1,000' wide and 2' deep. Thatcher Ck, near Copper Mtn. E and SE aspects around 8,500'. 

Avalanche Discussion

SNOWPACK IN TRANSITION

Our snowpack is on the doorstep of major change. We head into the second week of April with a mostly dry, wintertime snowpack on the ground, but that will be changing significantly beginning today. This transition will take place over the course of many days, and is likely to get pretty ugly at some point along the way. Let's look at how today may unfold:

Last night's storm brought a few inches of new snow to most parts of our forecast area. Temperatures cooled below freezing (32 F), but not by much. As today's sunshine and warm temperatures work their magic on the snow, wet snow problems will quickly follow. The fresh snow on top will rapidly melt, producing a number of small, surficial, wet loose avalanches. The meltwater from this melting snow will also be pushed into the snow underneath, accelerating the onset of deeper wet snow problems. As this warming and wetting of the snowpack progresses deeper into the snowpack, wet snow avalanches will become larger and more destructive. Wet slab avalanches will become increasingly likely over the coming days. Predicting the exact onset of wet slab avalanche cycles is borderline black magic, but we are definitely heading in that direction. We aren't likely to see widespread wet slab activity today, but I wouldn't be surprised to hear about an outlier or two happening today. 

If you're heading up high to avoid the heat today, you'll find a range of other problems in addition to the persistent slab problem described in problem 1 above. Small wind slabs formed during recent storms may remain reactive to your weight. Look for cracks shooting out from your skis or machine as an indication of an unstable slab. Very large cornices will be sagging and deforming with today's heat. Cornices are unpredictable, but you definitely don't want to be out walking and riding on them or to be hanging out below them on a day like today. Large cornices that fail can be very effective triggers for large slab avalanches on the slopes below. If you are up high today, remember that you'll have to come back down through the elevation bands to get out at the end of the day. Conditions will be more dangerous by this time.

The coming few days will be warm, wet and increasingly dangerous. The Avalanche Danger is MODERATEthis morning and is likely to be CONSIDERABLE tomorrow. If you're out late in the day or if you are playing on steep, sun-drenched slopes you may find yourself encountering a wet, ugly, unstable snowpack. Be prepared to step back from steep, consequential avalanche terrain if you are finding a thick stack of wet, mushy snow at the surface. And don't forget to pay attention to whats above you, wet snow avalanches will be happening naturally today. 

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