Bulletin d’avalanche

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
Voir sur la carte

Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
Open full map
Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dangerous avalanche conditions exist, especially in the western portion of this zone. Triggering an avalanche 12-18 inches thick is likely on wind-affected, upper elevation slopes. Avalanches are less likely—but still possible—in more sheltered terrain. Avalanches may be triggered from gentle terrain below, above, and to the sides of steep slopes. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Small storms since mid-December have slowly (sloooowly!) loaded an extremely weak, faceted snowpack, and now most of this zone has a soft, 12-14 inch thick slab atop a nasty persistent weak layer. The snowpack is teetering precariously close to the edge, but it has yet to take the plunge. Western portions of this forecast zone—in the Soldiers and near Dollarhide Summit for example—have received more recent snowfall. But by and large, this zone hasn't quite crossed the threshold into widespread instability.

    Although our area is famous for the excruciatingly slow loading of bad weak layers, that hasn't taught me to predict when the proverbial straw will break the camel's back. If anything, I've learned that it can be unpredictable. Will the 6+ inches of new snow that could accumulate by this afternoon, accompanied by a bit of wind, be that straw? 

    One thing is certain. Conditions are becoming increasingly dangerous and scaling back our terrain choices—today, and into the future—is essential. I'd avoid steep, upper elevation slopes—especially those that are exposed to the wind. Very steep, sheltered slopes also need an extra dose of caution. Pay close attention to signs of instability such as snowpack collapsing, cracking, and/or poor snowpack test scores. These will be sure-fire indicators that the new loading is bringing our weak snowpack close to the edge.

    ADDITIONAL DISCUSSIONWhile there's not a ton of wind accompanying today's snowfall, there could be enough to form small wind slabs in exposed terrain. I'd expect these to be much less of a concern than the persistent slab problem described above, but fresh wind slabs may be poorly bonded to underlying crusts leftover from the recent rain event. 

    (12/24/2020) Small, persistent slab avalanches near Dollarhide Mountain.

Avalanche Discussion

THE SLOW LOADING GAME

Although it wouldn't be as catchy on a license plate as "Famous Potatoes", our area is also famous for the slow, incremental loading of very fragile facet layers. These processes are really two sides of the same coin—which is that we live in a dry climate. Prolonged dry spells produce these persistent weak layers, and since small storms are more common than big ones in our area, they get loaded at a snail's pace. If our facet layers get loaded quickly by a large storm (as they occasionally do), the results are predictable. When we get the more common pattern of incremental loading, the predictability factor goes way down.

Years ago I had a close call that I attribute to the slow loading of a weak layer. My memory of the details is fuzzy (could be age-related), but it was a situation not unlike what we have now with a thin, slowly developing slab over a persistent facet layer. The consensus was that there just wasn't enough slab for widespread instability. I do remember one important detail about the day: there was only 4 inches of new snow. Our group triggered an avalanche, and while no one was caught, it was too close for comfort. We had totally underestimated the "straw that breaks the camel's back" factor.

In our northern mountains the loading since mid-December has been more substantial, and the warm and wet storm earlier this week produced an impressive avalanche cycle. But in our southern zones, instability has been less widespread and many folks have been exploring steeper terrain. Is today's snowfall going to be that straw? I still haven't learned how to answer that question. But I do know one thing: it's not a matter of "if" but "when" our weak snowpack will reach the breaking point. Today's storm could be it, or it could be the next one. Either way, I plan to dial back my terrain choices today. Getting surprised once was enough!

Want to catch up on what's happened this week? Be sure to watch our latest Weekend Update!

Régions couvertes