Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Wind slabs that formed with yesterday's new snowfall and wind remain a problem. You’re most likely to encounter a sensitive slab in upper-elevation terrain, particularly where they are resting on hard, icy surfaces. Triggering an avalanche on deeply buried weak layers is unlikely, but not out of the realm of possibility. Keep this problem in mind, particularly when traveling in steep, rocky, wind-affected terrain.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Yesterday, small wind slabs were reported along Mt. Taylor and other areas of the Tetons. I expect that these slabs grew in size and extent as wind speeds increased throughout the day and overnight. This problem will be most common in alpine terrain and at upper elevations where it remains possible to trigger slides on slopes over about 35 degrees in steepness. The slabs could be more sensitive to triggering where they overlie hard, wind-polished surfaces or crusts. If you see cracks shooting out from your skis or sled, consider where even a small avalanche could carry you before riding that really steep slope.  In the alpine terrain of the Tetons, spindrift trickling down cliffs and cross-loaded into narrow terrain features often forms slabs, as well as on the aprons below. Avoid steep slopes where you find these indications of recent wind loading. 

    ADDITIONAL DISCUSSION

    In areas that are not affected by the wind, yesterday's snow poses a different potential hazard. The forecast is calling for cold temperatures but clear skies. As we transition to spring, the sun continues to move higher in the sky and increase its input to the snow. I'd expect to see small, natural loose snow avalanches running in steep, rocky terrain over the next several days. These sluffs will also be easy to trigger if you're riding in steep terrain, particularly where stiff surfaces exist. This type of instability can be particularly pronounced in the very steep and rocky couloirs that are common to the Tetons.

     

     

    2/14/23

    Fresh wind slab cracking on Mt. Taylor at 8,500'.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    Triggering a 2-4 foot thick persistent slab avalanche on weak snow deeper in the snowpack is unlikely, but not impossible. You'll do well to keep them in mind and continue to factor them into your decision-making. It would take a dose of very bad luck, but you could trigger a large avalanche in very steep (over 35 degrees), alpine terrain that is more likely to have thin spots where your weight may reach the weak layers.  The weak layers we've struggled with most of the winter have not gone away, but they've become less reactive to the weight of a skier or rider over time. Due to their depth in certain areas, they've also become very difficult to impact with your weight. 

    Triggering a persistent slab avalanche is unlikely, but could be found in terrain with the following characteristics:

    • Steep and Southerly: slopes in prime-time avalanche terrain around 35-45 degrees ranging E-S-W on the compass.
    • Wind-affected: heavily wind-loaded by past or recent wind events.
    • Alpine flavor: complex, windswept terrain with rock ribs, cliff bands, or convexities.

    Deep Persistent Slab: In addition to the persistent slab problem type, weak snow near the ground persists, primarily on the southern half of the compass in the middle and upper elevations. This layer is considered dormant at this time with the last activity observed on January 16th. 

    (2/11/2023)

    Teewinot 10,300' SE aspect. Snowpit where we experienced large collapse. No cracking. Great example of why to avoid thin, shallow areas. 

    Photo: Drinkard

Avalanche Discussion

It Depends

Today will be a beautiful (albeit chilly) day in the mountains; sunshine and soft snow most everywhere you look. But don’t let the picture-perfect weather today, and throughout the next few days, lull you into thinking that the snowpack is perfect too. We tend to think that instability tapers off after an initial storm event—and sometimes, it does. The other side to this coin is that sometimes, it depends.  With shifting winds, temperatures, and added solar input, instability can ebb and flow, remain for far longer, and often increase days after a storm has passed. Unlike persistent slab problems, the stability of wind slabs can change rapidly — in both directions. Winds blowing out of the N continued to transport snow last night. This wind increased the thickness and the distribution of the slabs that formed yesterday. However, these slabs have now had some time to bond to the surfaces that they were deposited on. So, what does that mean for you? 

If you were out yesterday and you go out again today you'll probably notice a few things: the wind slabs you encounter will be thicker than what you saw yesterday, but they may be showing fewer signs of obvious instability. Without a persistent weak layer, wind slab stability can increase relatively quickly. But as these slabs have had time to bond to the snow they are sitting on, they were also growing in size due to the ongoing winds. As you head out to enjoy the snow, keep this variability in mind and frequently check in to see how the new snow is bonding with the old snow surface. Practice safe travel habits and conservative decision-making in the backcountry. This applies particularly to upper-elevation terrain that is easier to access, but we get less evidence-gathering and reassessment time (i.e. JHMR side-country). Picture the consequences of being caught in a slide in the terrain you are traveling in, not just the reward of riding great fresh snow. 

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