Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Wed
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 7 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

At upper elevations, the combination of new snow and wind will create sensitive wind slabs, and danger may rise by the end of the day. Deeper, human-triggered slab avalanches are also possible. These slides have the potential to fail near the ground, sending the season’s snowpack cascading downhill. Sticking to lower angle terrain not affected by the wind and avoiding areas where snow cover is thin are the best ways to reduce your risk.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Today’s storm will bring 4-6” of new snow to this zone, with another 1-2” falling overnight. Light to moderate winds blowing out of the western half of the compass will build slabs with this new snow. Wind slabs that you encounter today will likely be isolated to exposed, upper elevation terrain. These slabs will be more sensitive to your weight where they are sitting on icy crusts or slick, alpine surfaces. You can decrease your exposure to this problem by avoiding slopes with obvious signs of wind drifting.

    Be aware that if you trigger one of these slabs it may step down to weak layers buried more deeply in the snowpack as it travels downhill, triggering a very large, destructive avalanche. This persistent slab problem is described below.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    The month of January has brought above average amounts of precipitation to this zone. This snow has bonded well to itself, creating a strong 3-6 foot thick slab. If that were the entire story we wouldn’t have much to worry about. But (there’s always a but), this thick slab of snow is sitting on top of weak snow that is buried near the ground.

    Unfortunately, we don’t have good tools to help us forecast for these types of deeply buried weak layers. We can see that the snowpack structure isn’t great (picture a large, sturdy house built on a foundation of sand), but we can’t predict exactly when or where you might affect the weak snow underneath or how long it will take for this problem to heal.

    When dealing with deeply buried weak layers, here are two good approaches for reducing your risk:

    1. Avoid likely trigger points: You’ll be most likely to impact these deep weak layers in areas where the snow cover is thin, like near rocky outcrops. Heavily wind affected areas where the wind has created a patchwork of scoured and loaded slopes are also more likely to be problematic.
    2. Keep an eye on the terrain you are traveling through and underneath: Avalanches are most likely on slopes between 35-45 degrees of steepness. However, persistent slab avalanches can be triggered remotely — from below or to the side of steeper slopes.

Avalanche Discussion

Each winter we are faced with a different snowpack when we head out into the mountains. It's easy to get lost thinking only about the powder you are riding through, but pause for a moment and try to zoom out a bit. I like to think about the snowpack as a record of a season’s worth of weather, written in snow and ice. Thinking about it this way helps me to understand the snowpack as a dynamic animal that exists on a longer timeframe, instead of a static, stationary object.

Some years are marked by generally good stability with relatively easy to assess and manage avalanche problems. It snows and the wind blows, we give the wind slabs a few days to heal, and bam, we’re back out in avalanche terrain. Other years have us traveling through the mountains with our tails tucked and the hairs on the backs of our necks raised. All...season...long. Many days pass without snowfall, the likelihood of triggering avalanches decreases, but we’re still traveling conservatively knowing that the possibility of triggering large, destructive avalanches is on the table. If you’ve been tuning into the forecast this season, you know that we’ve found ourselves in the later category. 

In our northern areas, where the snowpack is deeper, triggering an avalanche involving weak snow near the ground is less likely, thanks to the thick slab of snow on top of it. Picture a well-armored, sleeping dragon — you can walk in a lot of places without waking up the beast, but if you find the chink in her scales (thin trigger point), you’ll find yourself facing an unsurvivable problem.

In our southern areas, where the snowpack is thinner, we are dealing with the flip side of this equation. Avalanches here will be smaller, thanks to the thinner slab that would be involved. But, you’re more likely to find a trigger point because the weak layers are closer to the surface. And notice that I said “smaller”, not small. The consequences of triggering one of these slides could be very high, particularly in areas where you would be carried through trees or swept into an abrupt terrain trap where avalanche debris can pile up more deeply.

To complicate matters, both of these persistent slab problems are capped with a few generations of recent wind slabs that are variably thick and variably sensitive to triggering. Is this all starting to sound complicated? Well, good. That means I’m doing a good job of painting the picture for you.

Régions couvertes