Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Look for relatively small, but reactive wind slabs in exposed terrain at upper elevations. Cracks shooting out from your skis or machine are a clear sign of an unstable slab. Periods of sunshine can quickly produce wet snow problems. Most wet snow slides will involve only the recent snow, but deeper wet snow issues can't be ruled out in areas where the underlying snowpack remains saturated from rain on Wednesday and Thursday. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    You'll find up to 2 feet of recent snow at upper elevations in this zone. The fresh batch of small wind slabs that formed in this zone yesterday were easy to trigger (photo at right/above). These slabs will remain reactive to your weight today, but should be small and relatively easy to identify and manage. Older slabs that formed at the start of the storm have had some time to bond, but you won't be able to identify them visually thanks to the new snow on top. You're much less likely to trigger one of these, but they are significantly larger than the most recent batch of slabs. 

    Help yourself identify and manage this problem by paying close attention to the snow you are traveling through. Conditions will change quickly as you climb in elevation and as you change aspects. The slope-to-slope complexity increased significantly during this storm, and the snowpack still needs some time to sort itself out. If you are entering avalanche terrain, you are accepting the uncertainty related to these changing conditions.

    (4/6/2024)

    This thin wind/storm slab was intentionally triggered on a NE-facing slope at 8,900' at the southern end of the Banner Summit zone on Saturday night. 

    Photo: Ben VandenBos

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    We will see another day of variable cloud cover. It does not take much April sunshine to melt fresh snow. As the sun pops out and warms and melts the new snow, wet snow problems can quickly turn on. Most of today's wet snow avalanche activity will involve only the snowfall from the past few days. However, the underlying snowpack is still saturated from intense rainfall on Wednesday and Thursday. Slides that gouge down into wet snow and flank out as slabs will be much larger, more destructive, and less predictable. 

    Conditions change rapidly in the spring. The snow can go from dry to wet in the time it takes you to eat lunch. If the sun is out, even for brief periods, spend a little time thinking about the snow you are moving through and the snow on the slopes above you. 

    (4/6/2024)

    Wet loose avalanches observed in Meadow bowl in the Sawtooths on Saturday afternoon.

    Photo: Ben VandenBos

Avalanche Discussion

UNCERTAINTY AND VARIABILITY

An intense series of storms this week brought significant rain to much of our terrain. Temperatures have gradually cooled since Wednesday and the rain/snow line has dropped with them. Friday and Saturday's precipitation fell entirely as snow, even at valley bottoms. When you head into the mountains today you will find wildly variable conditions as you climb in elevation and change aspects. Read on. 

At lower elevations, the majority of the recent moisture fell as rain, with a few inches of snow at the tail end Friday and Saturday. The snowpack here has had some time to drain and refreeze and triggering large slides at lower elevations is unlikely. However, if you're encountering a wet, mooshy snowpack, think about the consequences of triggering small wet snow avalanches.

As you climb into middle and eventually upper elevation terrain, you will see snow totals increasing significantly. Most of our upper elevation terrain stacked up 2 or more feet of snow since Wednesday. Strong winds blowing out of the S/SE accompanied precipitation initially. Winds picked up a bit yesterday and shifted to blowing out of the NW. A new generation of wind slabs built in upper elevation terrain. These fresh slabs will be easier to trigger but much smaller than the huge slabs that formed on Thursday. The older, much larger slabs have had more time to bond and will be less likely to slide. However, at upper elevations where these slabs rest on weak surfaces like facets and crusts they may remain reactive. As a reminder: skiers in the Boulders (on Galena Peak and Lorenzo) were triggering small wind slabs at the start of the week, before therecent storms. 

It will not take long periods of sun to bring wet snow problems to the table. 15 minutes of direct sun can radically transform fresh snow at this time of year. The loose wet and wind slab problems described above are taking place on top of a snowpack that remains wet from the recent rains. It will take some time to drain and refreeze the snowpack after the drenching it received on Wednesday and Thursday. We put a thick, snowy blanket on top of this warm, wet mess with colder snow on Friday and Saturday,  which helps to insulate the snow below and slows the rate at which the snowpack refreezes. 

Upper elevation rains on Wednesday and Thursday left a slick icy crust that is now buried by a foot or more of snow in most locations. Avalanches that fail within the recent snow will run quickly downslope on this crust. 

Manage the complexity, variability, and unpredictability posed by our transitional snowpack by building a wider safety margin into your travel plans today. Pay attention to the snow you are moving through, the snow on the slopes above you, and the snow you will have to move back down through at the end of the day. Watch the cloud cover and pay attention to how much snow is being melted. Be ready to step back from the plans you make, and have an exit strategy if things start to melt down. The Avalanche Danger is MODERATE and human-triggered slides are possible. Don't take that as an invitation to turn your brain off. 

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