Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
Open full map
Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Several days of snowfall and moderate winds have created dangerous conditions at upper elevations. Despite poor visibility yesterday, we saw several natural slab avalanches large enough to bury people. Avoid steep, exposed slopes with drifts or stiff snow on the surface. Natural loose snow slides (sluffs) are possible, especially if the sun pokes through the clouds. 

Problemi valanghivi

  • Wind Slabs

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

    With at least a couple feet of fresh snow in recent days, it doesn't take a lot of wind to form slabs. Yesterday, we saw sizable natural avalanches in alpine terrain in the Smoky Mtns (video to right/below, Observation), and snowfall and wind continued since then. Expect to find widespread wind slabs in exposed upper elevation terrain and in cirques beneath large cliff bands. Watch for and steer clear of slopes with drifting and with cornices on the ridges. 

    ADDITIONAL DISCUSSION:On very steep slopes, natural and human-triggered loose snow avalanches (sluffs) are possible. Yesterday, I saw a lot of sluffing and small cornice fall, and some of the small slides triggered sizable avalanches as they moved downslope. If the sun pokes through the clouds today, expect to see some natural loose snow avalanches. This problem is fairly simple to manage—be aware of the terrain above you, especially if it's sunny. Remember that even small slides can have high consequences if they carry you through rocky, treed terrain or push you down into a terrain trap like a gully or a creek bed.

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    3

    In this zone, the December facet layer is buried beneath a very dense, 3-4'+ slab. A unique characteristic of this weak layer is that despite having a crushing amount of weight above, it is not getting "squashed" like a more normal layer of facets would.  When a layer is buried this deeply, stability tests are time-consuming and really don't work that well—but don't worry, we did the work for you.

    It would take being in the wrong terrain, as well as a dose of bad luck, to trigger this layer. But if you did trigger a deep slab, you'd need all the luck in the world to survive it. So what's the wrong sort of terrain? Steep (over 35 degrees), rocky, wind-affected, "prime-time" terrain. You can avoid most risk of triggering a deep slab by sticking to sheltered, mid-elevation slopes where a more uniformly deep snowpack exists.

    (2/9/2021) A natural deep slab avalanche on McDonald Peak in the southern Sawtooths. It occurred last Sunday during the ongoing wind event.

Avalanche Discussion

Naps, Hibernation, and Dormancy

The persistent weak layers that produced extensive natural and human-triggered avalanche activity in December and January are finally showing signs of going to sleep. Unfortunately, they aren’t “out cold” yet; they appear to be stuck in limbo.

Think back to a time when you were listening to a boring teacher or professor’s lecture on an early morning when you didn’t get enough sleep the night before. The drone of the speaker’s voice continues, you are not interested, and your head begins to bob and then snap back up as you fight the urge to fall asleep. This is how our persistent weak layers are currently behaving.

When you were falling asleep in class, someone gently touching your shoulder may or may not have been enough to get your attention; this reaction (or lack thereof) is akin to the past several days of low-density snowfall falling on many slopes. However, what if your instructor poked you hard in the ribs with a pencil? You’d instantly snap out of your partial-sleep mode and be more than a little peeved, much like our weak layers on slopes where the wind is rapidly forming stiff drifts and wind slabs, or where small loose snow avalanches are running downhill.

Until it stops snowing and blowing for an extended time, I expect the persistent weak layers on some slopes to be susceptible to a pencil poke in the ribs. The difficulty lies in:

  • Which slopes are nodding off to sleep, and which slopes are “out cold”?
  • How hard is it to poke the weak layers on the slopes where they are still nodding off to sleep? How deep is the weak layer buried?
  • If I wake one of the sleepy students/weak layers up, will it be a meek 80-pound student who tells me off or a 280-pound behemoth who gives me a royal beatdown?

Our snowpack has become quite complex in the past 3 weeks, and it's nearly impossible to answer those questions on a slope-scale unless you’re an experienced professional studying and sampling the same slide paths day in and day out. As most of us don’t have either the luxury or experience to do so, we are forced to travel a little more conservatively than we’d like to give ourselves a healthy safety margin. As always, I encourage you to think about the consequences of triggering a sizable avalanche before committing to riding or skiing large avalanche paths.  

Regioni coperte