Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

You can trigger avalanches large enough to bury you on many slopes today. A storm brings up to 17 inches of snow by 5pm and sustained strong winds. Avalanche danger will rise to become very dangerous throughout the day.  Avoid traveling on or underneath slopes steep enough to avalanche. Slides can be triggered from long distances away from steeper slopes and can run into gentler terrain below. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–3

    Several weak layers are buried within the upper 2 feet of the snowpack. With the additional 17 inches of snow that will fall and strong winds throughout the day today, more stress is being added to these weak layers. Multiple human-triggered avalanches involving this snow were reported in the past 10 days (Profile drainage, Alturas Lake Creek, near Dollarhide Summit). This weak snow has produced avalanches on both shaded slopes and slopes facing the sun. On sunny slopes you'll find a sun crust with associated facets. On shaded slopes you'll find a few thin rain crusts with small facets sandwiched in between. 

    This weak layer is highly variable. On some slopes it is well bonded, while on others it is producing large avalanches. You may find good stability on one slope and then trigger an avalanche when you change to a nearby slope. Cracks shooting out from your skis or machine are a clear sign you've found an unstable slab. The human-triggered slides that have failed on this layer have been triggered from a distance (remotely). 

    ADDITIONAL DISCUSSION - DEEP PERSISTENT SLAB: The weak layer that produced widespread avalanche activity in January is now deeply buried here. If you dig down, you'll eventually find it buried underneath a very dense 3-5 foot thick slab of snow. Triggering one of these monsters is unlikely, but the result would be catastrophic. The most likely terrain for making one of these beasts is steep, rocky, wind-affected terrain where the snowpack has thinner spots that give you access to the weak layer. You can watch a video describing this problem here.

  • Storm Slabs

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

    The ongoing storm will bring up to 17 inches of new snow and sustained strong winds to the western end of this zone. Expect to find a range of problems involving this new precipitation. At upper and middle elevations, you'll find reactive wind slabs large enough to bury you and you may be able to trigger loose snow avalanches that run fast and far on weak, slick surfaces. Natural sluffs will run in the steep, wind-exposed terrain of the Sawtooths down to aprons. In sheltered middle elevation terrain, expect to easily trigger slides involving all of the new snow that may have a loose characteristic to them, or be more consolidated slabs. Enough recent snow will fall that these new snow avalanches will be large enough to bury you. Importantly, natural and triggered slides involving the new snow can trigger the much larger, more destructive persistent slabs described below. 

Avalanche Discussion

A winter storm will bring up to 17 inches of new snow to the Sawtooths & Western Smoky Mtns Zone by 5pm tonight, but there's a lot more nuance to how this storm will impact the snowpack. Avalanche forecasting at a regional scale is an imperfect science — we are forced to tell you what will happen across wide geographic areas that may be impacted by significantly different weather. Our current storm is riding in on a NW flow, meaning it will drop significantly more snow in the western and northern portions of this zone than in its southern reaches. Western locations like Williams Peak and Skeleton Creek will receive 17 and 15 inches of snow respectively, while the more southern Vienna will receive just around a foot of snow. 

In the southern portion of this zone, the new snowfall totals coupled with the sustained strong, westerly winds will be the main architects of new instabilities in the snowpack. Even foot of snow is enough to create avalanches running on the new / old snow interface that can be large enough to bury you. Add in sustained strong winds that can load even larger slabs into starting zones, and these slides definitely will be large enough to bury you. At upper and middle elevations, you'll find reactive wind slabs and you may be able to trigger loose snow avalanches that run fast and far on weak, slick surfaces. In sheltered middle elevation terrain, expect to easily trigger slides the new snow that may have a loose characteristic to them, gaining mass and speed as they run downhill. Importantly, natural and triggered slides involving the new snow can trigger the much larger, more destructive persistent slabs.

Now, take these conditions, but imagine them with a third more of the amount of snowfall in the northern and western portions of this zone. Expect each of these same issues to be worse here. This means larger wind slabs, more snow running in loose snow avalanches, and most importantly more load onto the existing persistent slab problem. Large natural persistent slab activity will become a concerning possibility here throughout the day, with the potential for slides to break deep into the snowpack and run to valley bottoms. While the avalanche danger is HIGH across this zone, just know that depending on where you head out today, you may find two, or a few, different shades of red. 

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