Bollettino valanghe

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Sawtooth Avalanche Center
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Pericolo valanghe

Sat
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Very large avalanches are almost certain. Avoid all avalanche terrain. Stay off of and out from below steep slopes—slopes steeper than about 30 degrees. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

The backcountry Avalanche Warning does not apply to the HWY 21 avalanche program.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    3–4

    Huge natural avalanches are very likely to fail on buried weak layers. Snowfall over the last ten days built dense 1-3 foot thick slabs and left many slopes teetering on the brink. Today's storm is the final nudge that is likely to push the snowpack over the edge. 

    A dry, cold February built a variable array of weak layers on all slopes (sugary facets or crust + facet combinations). Any avalanche that involves these deeply buried layers will be very large and destructive, capable of clearing trees or destroying a wood frame house. Some of these slides will be thousands of feet wide and most will run "full-path" including hundreds of feet into gentle or flat terrain. 

    The only way to manage this problem is to avoid avalanche terrain. This includes meadows that are well away from the base of any steep slope. Avalanches may be triggered from large distances—from gentler terrain above, below, and to the sides of steep slopes.

    (2/28/2023) NE face of Copper Mountain at 8,400'. This avalanche appeared to be remotely triggered by a skier from above. This crown in sheltered terrain (great skiing and riding conditions) is an excellent example of a slope that did not need wind loading to become unstable. 

  • Storm Slabs

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

    A powerful storm will bring about a wide array of new snow avalanche problems, including storm slabs, wind slabs, cornice failure, and loose snow avalanches. Snowfall rates of 1-3 inches an hour are expected. Storm slabs will grow in size and fail naturally throughout the day. These avalanches will be larger and more dangerous where the wind is piling snow into dense, thick slabs at upper elevation. Cornices will fail, and loose snow avalanches will be a near constant occurrence.

    Warm temperatures, wet snow, and/or rain this afternoon adds a sinister twist. Today's storm snow is likely to be "up-side-down" particularly at warmer middle and lower elevations. Dense snow or rain-on-snow will form top-heavy slabs that are likely to fail, even in areas that are entirely sheltered from the wind.

    New snow avalanches of any sort will be extremely dangerous on their own, but they also provide numerous triggers for the massive destructive avalanches described in Problem 2 below. 

     

    (3/7/2023) The crown of this remotely triggered avalanche is in fairly gentle terrain, but the slope below is steeper. Several recent avalanches behaved similarly, pulling into flatter terrain above steep slopes. Lake Ck drainage, NW 8500'.

Avalanche Discussion

Today's a day to stay out of the way. This large of a storm would likely prompt HIGH danger on its own, but to make matters worse, it's all landing on an incredibly weak snowpack. The combination of the two will produce massive, destructive avalanches.

This avalanche cycle will not be confined to the backcountry. At least five large avalanches crossed Warm Springs Rd last week, some depositing piles of snow and trees up to 30 feet deep, and these were before the storm. Today, I expect to receive reports of avalanches blocking roads, crossing walking paths, and damaging buildings. Valley temperatures will climb above freezing, aiding in the release of numerous top-heavy storm slabs or wet avalanches and increasing the odds of dangerous roof slides.

Avalanche conditions are very dangerous this morning and will worsen throughout the day. Avoid all avalanche terrain, including flat terrain like walking trails or roads that traverse beneath steep slopes.

Regioni coperte