Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Triggering a large avalanche remains possible where the wind has stiffened the snow. While less likely, there is a small chance of triggering an avalanche in very steep, wind-sheltered terrain. Small, natural or human-triggered, wet loose avalanches are likely on very steep, sun-drenched slopes. 

Problemi valanghivi

  • Persistent Slabs

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

    Skiers and riders triggered several slab avalanches in the past week. All involved persistent weak layers (crusts and facets, facets) in the upper 1-2 feet of the snowpack. Some were triggered remotely—from gentler terrain above, below, or to the side of the slab (photo, photo). Yesterday, a local professional reported snowpack collapsing near 9000' in the central Smoky Mountains. Given the recent avalanche activity and continued "red flag" signs of instability, we're not out of the woods yet. 

    You are most likely to trigger a persistent slab avalanche on shadier, very steep slopes where the wind has built a stiffer, denser slab. Recent wind-loading is most pronounced near and above about 9000' in elevation. While less likely, triggering slabs in sheltered terrain can't be entirely ruled out.

    You can significantly reduce the odds of triggering a large slab avalanche by sticking to slopes less than about 35 degrees that are typically sheltered from the wind. 

    ADDITIONAL DISCUSSION: Small, isolated wind slabs formed over the weekend. While thin and relatively narrow, they may be large enough to knock you off your feet or sled. Think about the consequences of being caught and carried by a small avalanche before committing to serious or extreme terrain. 

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    The threat of natural and human-triggered wet avalanches will rise during the day. We should consider a few specific wet loose avalanche scenarios:

    • Thin, surficial slides: Small, thin slides are likely in very steep, rocky terrain that is sheltered from the wind and directly faces the sun. I saw a few of these events yesterday afternoon (view observation), and the Sawtooths are full of this type of terrain. This hazard will follow the sun around the compass, beginning on E-SE aspects this morning, moving to S-facing slopes by noon, and impacting W-SW aspects this afternoon and evening. 
    • Larger, "gouging" slides taking out much of the snowpack: Where the snowpack is less than about 2 feet thick, some slides could involve the entire snowpack. These are most likely on very steep, rocky slopes that are sheltered from the wind. The video to the right/below shows how powerful these avalanches can be. Imagine trying to escape that gloppy mess while it's flowing!
    • Either type of wet loose avalanche could trigger the persistent slabs discussed in Problem #1 above, especially on slopes on "the margins" (more easterly and westerly aspects where the persistent slab and wet loose problems overlap). 

    Wet snow stability can change rapidly; think minutes rather than hours. The steep slope that you safely traveled on or beneath in the morning may not be stable later in the day. With last night's weak freeze and today's hot, sunny conditions, crusts could break down quickly. If you're sinking more than a few inches into a wet snowpack that resembles the oatmeal you ate for breakfast, you'll want to stay off of and out from underneath steep slopes. Pay attention to the terrain above you in your travels, and do not linger below very steep slopes longer than needed; wet avalanches frequently release on their own. Plan your day carefully to avoid traveling in or above terrain traps, especially during the afternoon.  

Avalanche Discussion

THE BEGINNING OF A TRANSITIONAL PERIOD

With last night's weak freeze and warm, sunny weather in-store today, meltwater will move down into the snowpack. The unpredictable persistent weak layers in the upper snowpack (crusts, crusts and facets, and facets) have already caused problems and will not like getting wet for the first time. I'm not expecting to see the world come crashing down today, but I do expect to see or hear of an avalanche or two that make me think "huh, that's interesting." Today's "odd" or "rogue" avalanches will probably become more common during the heatwave in the coming days.

When you're planning where to go play in the sun, remember that weird weather makes weird avalanches. The variable, messy layers in the upper snowpack are going to be tested by this week's hot weather and resultant meltwater; predicting how the snowpack will react is even more difficult than predicting how it would handle last week's snowfall and wind-loading. The warm weather will help these layers heal in the long term (many days/weeks), but all bets are off in the short term (hours and days). Unfortunately, the only way to manage uncertainty is avoidance. Stepping back from very steep, consequential terrain is the prudent play wherever water is moving down into the snowpack. Let the heatwave run its course, watch the show, and postpone those big adventurous days in the mountains until we get through this transitional period. 

Regioni coperte