Bollettino valanghe

Togwotee Pass

Bridger-Teton Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
Senza grado
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Triggering a large, dangerous avalanche remains likely—especially in wind-affected, upper-elevation terrain. Strong winds have created sensitive drifts in the upper elevations and have added increased weight to buried weak layers and poor structure within the snowpack. Expect to find these in atypical locations, thanks to the strength and direction of the wind. A report came in yesterday regarding another remote triggered avalanche, this one on the East face of Mt. Leidy. Three days ago a large avalanche was remote triggered on Angle Mountain. While today's temperatures will remain cool, any period of sun this time year will drastically alter the snowpack and its stability. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Two primary layers of weak snow exist in the top meter of the snowpack. Yesterday in my travels on West Angle, and near a remotely skier-triggered avalanche, the poor structure was apparent once I dug down into the snow. The most recent snow sits on top of a myriad of facet crust combinations that have recently become reactive, on Angle Mountain and Mt. Leidy. Failures within snowpit tests are easy to obtain and avalanche slopes should be approached with a high level of skepticism of whether the risk is worth the reward. We don't often deal with persistent weak layers so late in a season, and it definitely requires a mindset shift. Triggering a 2-3+' thick persistent slab avalanche will remain a possibility this coming week. 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. 

    Deeper weak layers formed earlier in the season composed of crusts, facets, and depth hoar remain a concern. Triggering a wind slab or persistent slab on the March 20th interface could step down to these layers resulting in a large to very large avalanche.

     

     

    Recent size D2 Avalanche on Angle Mountain

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Triggering a large avalanche is most likely where the wind has drifted the snow. Yesterday's east winds convoluted an already complex problem, loading atypical areas and thus connecting more terrain to our avalanche problems. 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 may step down into buried weak layers (see above), producing an even more dangerous avalanche.

     

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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