Lawinenlagebericht

Tetons

Bridger-Teton Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Human-triggered avalanches are possible today due to weak layers of snow buried over the weekend and wind slabs that have developed since. If triggered, either type of avalanche could be large enough to bury a person. Choose terrain carefully and evaluate slopes for the existence of wind drifted snow or buried weak layers. When in doubt, seek out lower angled slopes sheltered from the wind. 

A large avalanche triggered on Mt. Taylor three days ago illustrates scale of the potential hazard. Skier-triggered avalanche on Mt. Taylor.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    Last weekend, a record-setting storm loaded a significant slab onto a layer of weak snow on the surface. That weak layer is now buried two to three feet deep, deeper in wind loaded areas, in the Tetons and Greys River zones. Multiple human-triggered avalanches, some of them triggered from a distance, have been reported on this weak layer. Triggering a slab avalanche 2-3 feet thick, possible thicker, on this layer remains possible, particularly in steep, rocky terrain. Dig, probe, and test the snowpack in a safe location to determine if this layer if present before committing to consequential terrain.

    DEEP PERSISTENT SLAB: In addition to the layer buried Jan 26 (see above), a deeper weak layer persists in middle and upper elevations on southeast through west aspects. Triggering an avalanche on this layer is very unlikely as this layer appears to be dormant; however, a very slight risk remains for larger loads such as another triggered avalanche or a group of people in very steep terrain to impact a thin spot and trigger this deeper weak layer. The resulting avalanche could be up to five feet thick or D3+ in size, in other words, large enough to easily break mature trees or destroy a truck. 

    (1/30/2023)

    Aerial view of a very large avalanche on the SE face of Mt Taylor, triggered by a party on the ridge. 

    Photo: Teton County SAR

  • Wind Slabs

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

    Moderate to strong westerly winds have moved low density snow onto lee slopes since the storm cleared on Monday, with some plumes observed at the ridgetops yesterday. Cold weather has, to some degree, preserved these slabs which may remain sensitive to human triggering today. These slabs may be hard and stubborn in some locations and softer and more sensitive in more sheltered areas. Look for cracking or hollow sounding hard slabs indicating soft and weak snow beneath.  Very steep, unsupported slopes or convex terrain are especially suspect.

    Wind affected snow takes on many appearances. Snow that looks like this typically harbor weak snow beneath a heavily textured, stubborn hard slab.

    Photo: Antonioli

Avalanche Discussion

Today, you'll note that the danger ratings have dropped from 3 to 2 on a scale that goes, very rarely, as high as 5. Last weekend, avalanche danger in the backcountry was rated 4, also known as High, and the danger was obvious. Record setting snowfall, some wind and an existing weak layer of snow on the surface created that level of danger. The danger was plainly obvious, and it was easy to understand the risks at hand, particularly given the evidence which included large natural avalanches. In the past few days, as skiers and riders have tested the snowpack, the feedback has been less clear, but it has been there; avalanches weren't occurring naturally but they could be triggered, though in fewer locations throughout the terrain. And lots of terrain, but not all, was ridden with no avalanches. The evidence for avalanche occurrences continues to taper today. Fewer signs of unstable snow will exist which is a good trend but this lack of obvious clues to unstable conditions could create a temptation to ramp up the risk taking. The bluebird conditions and warmer weather can play the siren song that lures the susceptible to go places they shouldn't go. Be sure to consider the recency of large avalanches, look for the buried weak layers and consider the consequences of being wrong, even if just a little bit wrong, before you commit to serious terrain.

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