Boletín de aludes

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

The avalanche danger will rise to CONSIDERABLE as the day heats up. Multiple days of hot weather were followed by warm, cloudy conditions last night—not good! Expect to find a wet, soggy snowpack on all but upper elevation, north-facing slopes. Small to large wet slides will be possible this morning and become more likely through the day.

Problemas de aludes

  • Loose Wet

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

    The past 3 days were the hottest so far this winter, and overnight temperatures have remained above freezing. The saving grace? The snowpack surface has still been freezing at night due to radiational cooling—a process that requires clear skies. Well, things took a turn for the worse last night. Increasing clouds yesterday evening were like throwing an insulated blanket over our warm, soggy snowpack—not good! With overnight temps staying in the upper-30s to 40 F, I'd expect that the snowpack this morning will have a surface shell no thicker than your Easter eggs.

    The past few days of hot temps have already increased the meltwater within the snowpack (read the Forecast Discussion below). A warm, cloudy night followed by more sunshine and heat today could be the nail in the coffin for our soggy snowpack. Expect the chance of both natural and triggered wet slides to increase quickly today. Many steep, sunny slopes have saturated snow to the ground, and the potential exists for large, dangerous wet slides gouging deeper into the snowpack.

    If you'd rather spend your Easter in wet, sloppy snow than looking for baskets hidden by an egg-laying rabbit and gorging yourself on Cadbury® chocolate eggs—then hop to it. I'd look for some way to get to upper-elevation, northerly-facing terrain (the only place you'll find dry snow) without traveling on or under steep slopes with a wet snowpack. We can't rule out the possibility of wet slab avalanches—especially today—and this necessitates a more conservative approach to managing the wet snow problem.

    ADDITIONAL DISCUSSION - WET SLABS: Wet slab avalanches are tough to predict, but we do know they are more likely when 1) Well-defined weak layers exist in the snowpack, and 2) During prolonged warm weather with little to no overnight freezing. Sound familiar? Spring doesn't always lead to a predictably stable snowpack (watch video from Galena Summit on Friday). Although wet slabs aren't likely, they should factor into your plans during this and subsequent warming events this spring. This isn't the year to be playing in steep, consequential avalanche terrain after little to no overnight freeze, and make sure to give yourself an extra margin of safety to be out of harm's way before the surface gets wet and mushy. 

    (4/4/2021) Several days of the winter's hottest weather were followed by a warm, cloudy night last night. With little to no freeze of the snowpack overnight, wet snow conditions will quickly become dangerous today as the clouds clear and the temps rise.

Avalanche Discussion

My favorite t-shirt features a snowflake and the statement "I'm complex." (My second favorite also has a snowflake, but says "All my friends are flakes.") While snow is always a complicated phenomenon, adding water to the mix takes it to another level. Fortunately wet snow stability can be boiled down to one simple concept: the more liquid water contained within the snowpack, the more unstable it is.

Water builds up within the snowpack when the melt at the surface exceeds the ability of the snowpack to drain it out the bottom or to freeze it within the snowpack. This is usually the case during these early spring, prolonged warming events. The snowpack is in a state of transition, and it hasn't yet established drainage pathways to prevent the build-up of meltwater. As the water content increases, the liquid water melts the bonds between grains and leads to cohesionless slush (think Slurpee). When little to no freeze happens overnight, the water factory works around the clock (in violation of union rules) and production goes into high gear.

Water content is highest near the surface of the snowpack where the melt occurs, which leads to wet loose avalanches. When the snowpack becomes saturated deeper than the surface layers, wet slides can gouge deeper into the snowpack. The elephant in the room is when meltwater accumulates in a snowpack with a well-defined slab over weak layer structure. In this scenario, the weak layer (facets, crust, etc) can lose strength and result in the release of a destructive wet slab avalanche (watch video from Galena Summit on Friday). 

In late spring and early summer, the temperatures are even hotter and it rarely freezes. Why does lingering mountain snow become stronger then? By this point, the snowpack has a well-developed drainage network. So even though meltwater production is in high gear and 'round-the-clock, the water flushes through the snowpack and the overall liquid content remains low.

Be sure to catch up on what happened this week—including windy weather and wild temperature swings—in Ben's latest Weekend Update.

PLEASE HELP US HELP YOU:  We want to learn more about how you use the Forecast and our products. Kelly Rice-McNeil (Eastern Oregon University) and Victor McNeil (Wallowa Avalanche Center) are spearheading a project to understand how you use avalanche center products and, ultimately, to improve them. Help us help you by taking 10 minutes or so to fill out a survey. Teaser: there is a little SAC-specific questioning involved - please participate and get your backcountry partners, friends, family, and clients involved! Google Forms link:  https://forms.gle/YwgEwHRnT4ucSF226  

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