Lawinenlagebericht

Tetons

Bridger-Teton Avalanche Center
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Lawinengefahr

Thu
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, dangerous avalanche remains possible—especially in wind-affected, upper-elevation terrain. Yesterday's east winds have loaded snow into non traditional start zones and wind slab avalanches may have the potential to impact buried weak layers in the top meter of the snowpack. 

While today's temperatures will remain cool, any period of sun this time year will drastically alter the snowpack and its stability. 

Lawinenprobleme

  • Wind Slabs

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

    A friend and mentor used to say that nothing good ever comes from an east wind, and yesterday was a great example of this statement. Over the past 24 hours, steady winds from the NE have formed wind slabs in atypical locations. These slabs were reactive to ski cuts and were anywhere from 30-45cm in depth. I also experienced a notable collapse while skinning up a recently loaded ridgeline. Triggering a large avalanche is most likely where the wind has drifted the new snow in upper-elevation and alpine terrain, and exposed middle-elevation slopes. Yesterday a backcountry traveler came across a large D2.5 hard slab avalanche near Shovel Slide on Mt. Glory. Expect to find wind slabs in both obvious locations (such as near ridgelines) as well as in atypical locations that are commonly sheltered from the effects of the wind. 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. Wind slab avalanches could break down into buried weak layers (see below), producing an even more dangerous avalanche.

     

     

    (4/4/2023)

    Hard slab avalanche 9,400' S aspect Mt. Glory. Yesterday's atypical easterly wind direction slabbed up many open slopes.

    Photo: Wyatt Sullivan

  • Persistent Slabs

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

    As we wind down and out of an extended period of stormy weather, our most recent persistent weak layer which was buried on 3/20 still warrants attention. The latest activity on this layer was reported on April 3 on Mt. Taylor - see associated photo. The distribution and reactivity of this weak layer 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 where the 3/20 layer consists 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 will remain a possibility this coming week. 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 a trigger 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. You can also choose to not enter this terrain and ski gentler terrain that limits your exposure.

    (4/3/2023)

    This large natural avalanche was observed on 4/2 on Mt. Taylor on a NE aspect around 9,800'.

    Photo: Jediah Porter

Avalanche Discussion

The past few weeks have featured a mid-winter powder euphoria, perhaps some of the best conditions of the season. Cold temperatures and consistent snow have satiated many, and while some are eager for spring the complexities of a mid-winter snowpack are front and center and we can't allow ourselves to let our guard down. While our snowpack is deep - my 320cm probe almost disappeared yesterday while probing around Wimpies in GTNP - weak layers lie within the top meter. Yesterday's NE winds hammered exposed terrain creating wind slabs in atypical locations, and tarnishing the sublime conditions. Though it may become a blessing in disguise as it will require the savvy backcountry traveler to sniff out sheltered terrain - out of the wind and also off of terrain plagued by our 3/20 layer. As we transition from this stormy period into the beginnings of some high pressure, we'll see colder-than-normal temperatures followed by a warming trend. Additionally, wind slabs now can be found across the compass rose from shifting wind directions, such that I would approach most terrain today as if it all has a shallow wind slab with some deeper than others. All with the potential to stepping down to our persistent weak layer. 

While the skies may be clearing, the reactivity of our persistent weak layer buried on 3/20 requires assessment and a mindset not typical for this time of year. Taking a step back and letting the dust settle on this storm is prudent, and will be difficult given the spatial variability of its reactivity. So rather than running towards your next objective, take some time and approach it with some assessment to avoid the slap in the face that mother nature can hand out so quickly. 

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