Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
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Pericolo valanghe

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

Avalanche danger will rise rapidly to considerable today as a strong storm impacts the area with new snow and strong winds. Human triggered wind slab avalanches are likely at mid and upper elevations. Natural avalanches are possible.

Avalanches could break deeper on persistent weak layers in the middle of the snowpack, resulting in larger, more destructive avalanches.

If you encounter natural avalanches or see shooting cracks around your skis or snowmobile, stick to slopes under 30 degrees in slope angle. 

 

Problemi valanghivi

  • Wind Slabs

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

    Winds for the past 24 hours were moderate from the southwest but increased in speed overnight. Very strong southwest winds will continue today with gusts into the 50mph range along ridgelines. 

    Wind slab formation was observed the past 2 days at upper elevations. This slab formation will continue today as more snow becomes available for transport.

    How much new snow falls today will largely determine wind slab size. If we receive the expected 4-8 inches today, expect wind slabs in the 1-3 foot range. 

    Strong winds often build wind slabs in unexpected locations like low on slopes and in cross-loaded gullies. Wind slabs can appear as smooth or rounded pillows, but this may not be obvious today as new snow will quickly bury and hide wind-loaded areas.

    If you see recent avalanches, shooting cracks, or collapsing, step back to slope angles under 30 degrees.

    (2/24/2024)

    Active wind transport of snow is visible in this photo. Snow is blowing off the edge of the cornice and loading the slope below.

    Photo: Payton Schiff

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–3

    There are a variety of persistent weak layers in the snowpack, including rounding facets near the ground, small facets above a crust in the middle of the snowpack, a thicker layer of buried near-surface facets above a crust, and buried surface hoar.  They have been laying dormant for the past 10 days, but the poor snowpack structure remains, and in the case of the facet/crust combination, has continued becoming weaker in some areas.

    The incoming storm will increase the load on these weak layers. Will this fresh load today tip the scale to where we start to see larger avalanches, especially on the buried facet/crust interface in the middle of the snowpack? Time will tell, but you don’t want to be the one to find out.  If you do trigger an avalanche on these layers, it is unlikely that you will see obvious signs of instability like whumfing, collapsing, or cracking before the avalanche occurs.

    Dig in the snow, and if you find weak snow around crusts, or loose sugary snow below a firmer slab, recognize the potential for a larger, more dangerous avalanche in these areas. Smaller avalanches have the potential to step down and trigger a larger avalanche on persistent weak layers.

Avalanche Discussion

Keep it simple today. New snow + strong winds = avalanches.

2-3 feet of snow is expected through Tuesday, with the bulk of the storm arriving tonight.  Winds throughout the event will be strong out of the west/southwest, with gusts in the extreme. This storm direction favors much of our forecast area for orographic lift and a winter storm that delivers snow.

How do we manage this new snow and rapidly rising avalanche danger? With patience. Elbert Despain was the mailman in the famed Little Cottonwood Canyon, infamous for avalanches well before the time of avalanche control. How did he manage to stay alive so long and not get caught in an avalanche? He would wait two days after a large winter storm before traveling through the canyon. In today's age, especially after a winter lacking in powder days, it can be tough to be patient, especially when the weekend is ending, or someone else might reach your spot ahead of you.

External factors cloud our decision-making, even when red flags of avalanche instability are obvious. By the end of the day today, signs of instability will be flashing in our faces.

Let us know what you are seeing in the mountains today by submitting an observation.

Ski and ride safe.

 

 

 

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