Lawinenlagebericht

Tetons

Bridger-Teton Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Triggering a large avalanche remains possible—especially in wind-affected, upper-elevation terrain were wind slabs have been failing on persistent weak layers. Yesterday a snowmobiler triggered an avalanche near Teton pass that was large enough to injury or bury a person. By midday expect wet loose activity around the southern half of the compass that has the possibility to entrain the recent storm snow in steep avalanche terrain. 

Despite the cold air temperatures it's April, so any period of sun this time of year will drastically alter the snowpack and its stability. Also as temperatures begin to warm, cornices that have been building all winter long will begin to decrease in strength. Limit exposure beneath these giants and give them a wide berth while traveling along ridgelines.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    Our current persistent and wind slab problems are loosely tied together in a complex relationship. Two layers reside within the top meter of the snowpack, the most recent culprit has been the 3/29 interface which has been associated with avalanches already this week - yesterday on B-Z Bowl (Phillips/Teton Pass) and on Sunday in GTNP. Weak snow surrounding the 3/29 interface has allowed wind slabs to propagate widely as seen in these two examples. Additionally, the 3/20 layer hasn't ridden quietly into the sunset just yet - and could have played a role in this reported slide on Monday on Mt. Taylor.

    The distribution and reactivity of these weak layers have been centered around SE and E aspects where facets have been found on top of a crust. However, human-triggered and a few natural avalanches have also been noted in NE-facing terrain consisting of buried near-surface facets. It's a complicated problem that isn't typical for April, and triggering a 2-3+' thick persistent slab avalanche still remains a possibility. Most accidents involving persistent weak layers happen as we ramp into and out of storm cycles, and we're just exiting the cycle now.  Examine this problem by digging into the snowpack in several locations to assess the layer's reactivity, as at this point in time the layer's feedback via collapses and natural activity may be limited, and it may just need provoking to impact the sweet spot. You're most likely to trigger a slide involving this weak snow on very steep slopes (steeper than about 35 degrees) where the wind has built slabs in recent days and weeks. In the Tetons, slabs also commonly form below cliff bands, on the aprons below steep couloirs, or at the base of cliffs where spindrift accumulates. Watch for evidence of windblown snow such as pillowed areas, dunes or ripples, or denser snow at the surface. You can also choose to not enter this terrain and ski gentler terrain that limits your exposure.

    Snowmobile triggered wind slab avalanche that failed on the 3/29 interface, as viewed from Pyramid. 20230405-SS-AMu-R2-D2-I East facing B-Z Bowl @ 9,200'. 

  • Loose Wet

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

    Temperatures will start out cold, but as the April sun pierces into the upper reaches of the snowpack it will begin to alter its stability. Yesterday was the first truly clear day following a cold and snowy week, and while the sun affected lower-elevation slopes the warming trend is set to kick in today. As the day warms it will be important to monitor solar aspects especially steep rocky areas. Point releases and rollerballs are signs that the snow is losing its cohesion. Our snowpack has several melt-freeze crusts near the surface which will act as excellent bed surfaces. Avoid traveling under steep solar avalanche paths during peak warming. 

    Low elevations began showing signs of Wet Loose activity Tuesday afternoon.

Avalanche Discussion

There is a saying that spring is a battle between winter and summer. While winter has been steadily winning rounds in this year's boxing match, it may be taking a seat as we begin a warming trend today that will likely begin to affect the stability of our snowpack.  As we transition from this stormy period into the beginnings of high pressure, wind slabs now can be found across the compass rose from shifting wind directions, all with the potential to stepping down to our persistent weak layer. You'll notice today that we pulled wind slabs off the problem list as their reactivity has been correlated to these weak layers, and we grouped them with our current persistent slab avalanche problem. However, make no mistake if you travel into the higher alpine terrain, specifically around GTNP, expect to find wind slabs in various forms from our shifting wind patterns and train of storms. Furthermore as winter sits down in the corner for a break, the emergence of the sun and rising temperatures will quickly destablize the surface snow. After a deep and long winter it's hard to imagine it's already the first week of April. Keeping that in mind, don't fall trap to winter's slumber and be aware of your surroundings even if you are seeking sheltered and drier snow - making sure you are out of the way and not under steep solar avalanche paths as the spring shed cycle begins. The same goes for cornices, give these a wide berth and be wary of hanging around slopes where these monsters lurk above you.

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