Lawinenlagebericht

Snake River Range

Bridger-Teton Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist last year abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Recent snowfall and strong winds make triggering a slab avalanche up to 18+ inches deep likely in steep and wind-loaded terrain above 9,000’.  Although less likely, some avalanches could break up to 3 feet deep in very steep terrain. Conservative terrain selection and avoiding steep, wind-loaded slopes are recommended today. 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Over the past 48 hours, around 10 inches of snow has fallen in the upper reaches of the Snake, accompanied by intense WSW winds. A trace amount of new snow is expected today. However, intense winds and various weak interfaces in the top portion of the snowpack may keep this snowpack on edge. Several layers, including recent storm changes in snow type as well as deeper crusts/facets, may remain touchy to human triggering today.  Soft slabs up to 18 inches deep will remain sensitive to the weight of a rider in very steep (>35°) and wind-loaded terrain above 9,000’. Less snow has fallen at lower elevations, though the wind has touched snow on almost every aspect and elevation. Thus, wind slabs will be smaller and isolated to very steep terrain at low elevations. Look for signs of instability, including cracking within the new snow or recent avalanches.

    Although less likely, larger avalanches up to 3+ feet deep could be triggered on steep and wind-affected slopes above 8,500’. Over the last several days, weak interfaces below older wind slabs have resulted in several large human-triggered avalanches. New snow and wind loading are stressing these deeper layers and could make them more sensitive to triggering today.Carefully assess the snowpack in wind-affected and very steep terrain to determine if the potential for deeper avalanches exists. Giving very steep and wind-loaded features a wide margin is the best way to manage this problem today.

    (3/21/2025)

    This avalanche was remotely triggered by a snowmobile yesterday in Mosquito Creek and is a good example of terrain where deeper avalanches involving older wind slabs are possible. NE aspect at 9,100'.  The avalanche failed on old snow around 2-3 feet deep.

Avalanche Discussion

Spring is a transitional time that can bring some wild storms and snowpack patterns to track. Enjoy some nice powder today (if you can find where the wind blew it all), but remember that reactive problems linger in the top portion of the snowpack. Human-triggered avalanches on these layers have been reported the last several days in upper elevation terrain and may not present themselves with obvious evidence other than triggering a large avalanche. Widespread instabilities and natural avalanches oftentimes don't present themselves in an easy-to-read pattern as a backcountry traveler in the spring. Storms can also be quite rapid and transition quickly between different snow types, warm temperatures, clear skies, and more. These changes can influence the surface slab of snow to be more or less reactive relatively quickly. Avalanches can occur on many interfaces, not just persistent weak layers. One example is "upside-down" storm snow, which fits what I found yesterday while riding. This means that the slab and weak layer are just composed of different snow crystal types from several days of snowfall. 

•Slab layers (denser) = small crystals, needles, and columns, rimed crystals like what was falling yesterday (but not graupel that ended this storm)

•Weak layers (low density and graupel) = larger crystals with little to no riming and graupel/ice crusts

This storm ended with some awesome large graupel (like hail), but most of the slab is composed of rimed crystals atop larger crystals with less riming. The type of snowfall depends on cloud temps—not surface air temps. High-density snow can fall at low temperatures, and low-density snow can fall at high temperatures. Overall, the amount of riming (i.e., high humidity conditions when snow crystal shapes become obscured by additional moisture clinging and freezing to the original crystal, usually accompanied by high winds) adds complexity, making for a solid slab if falling on weaker crystals, and especially with the addition of wind compaction with intense winds. Overall, there are things to watch moving forward: wind-loaded slopes with new snow and most low, mid, and upper-elevation slopes, with the warm-up arriving later this week. 

If you see avalanche activity today, please consider submitting an observation HERE. Observations allow everyone to gain a better and more complete understanding of conditions. Thanks!

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