Bollettino valanghe

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Sawtooth Avalanche Center
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Pericolo valanghe

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

In sintesi

Dangerous avalanche conditions exist. You could trigger large avalanches on many sheltered and wind-affected slopes. You could trigger avalanches remotely—from gentler terrain above, below, and to the sides of steep slopes. Naturally occurring loose snow avalanches are likely on slopes that face the sun. Seek out drier, colder slopes and choose lower-angled terrain to reduce your risk. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    We're dealing with a mid-winter-style snowpack. There are two distinct Persistent Slab problems to consider:

    1. "Fresh" Slabs: Yesterday, riders remotely triggered a large avalanche from a meadow 50 yds to the side of the slope. The slide broke over 1,000' wide and 2' deep (report). Sunday, SAC forecasters remotely triggered a large avalanche in this zone (video), and an observer heard two natural avalanches release near Copper Mtn. These avalanches failed on crust + facet combinations or thin layers of small facets in the upper 2 feet of the snowpack. Due to the variable weather in March, the distribution of these weak layers varies greatly from slope to slope and across the zone.
    2. Older, Deep Slabs: While it would take a dose of bad luck, triggering a massive 3-5 foot thick avalanche on older, deeply buried weak layers can't be ruled out. Yesterday, I observed this deep slab avalanche in the southern Sawtooths (report). It likely released sometime over this past weekend. One week ago, in the Frenchman Ck drainage near Smiley Ck, riders remotely triggered a slide that broke 4-5' deep and over 800' wide (report). While triggering one of these beasts is far less likely than the "fresh" slabs above, the consequences would be devastating.

    These Persistent Slab problems are tough to manage. You may or may not see obvious signs of instability on unstable slopes, depending on the depth of the weak layer. Multiple skiers or riders might play on a slope before it avalanches. Reduce your risk by staying off (and out from beneath) slopes steeper than about 35 degrees.

    ADDITIONAL DISCUSSION: There are a host of other avalanche problems to consider, including loose snow avalanches, wind slabs, and cornices. While these may be dangerous on their own, they also provide large triggers for the Persistent Slab problems described above. Read more about these in the Forecast Discussion below. 

    (4/5/2023) This avalanche was remotely triggered by two snowmobilers from a meadow 50 yds to the side of the slope. The slide broke over 1,000' wide and 2' deep. Thatcher Ck, near Copper Mtn. E and SE aspects around 8,500'. 

Avalanche Discussion

Many of us are used to a more uniform, stable snowpack this time of year, one that's seen multiple waves of meltwater followed by a freeze. So far, the abnormally cool and snowy spring has held off this transition, and our snowpack is in mid-winter form. Many slopes harbor a highly variable mix of facets and crusts in the upper 2' of the snowpack. Trying to tease out patterns of which slopes remain unstable is tricky at best and dangerous at worst. Yesterday's snowmobile-triggered avalanche (report) came after a day of riding with no obvious signs of instability. Then there's this deep slab avalanche (photo) and Friday's remotely-triggered slide in the Frenchman Ck drainage near Smiley Ck (report). Both are sobering reminders that our older, deeply buried weak layers are still in play.

While most of the snowpack is stuck in winter, today's weather will edge more toward spring. With dynamic weather comes a host of secondary avalanche problems to consider:

  1. Wind Slabs: Look for these in exposed middle and upper elevation terrain (photo). Any wind slabs that you encounter may be perched above weak facets and/or crusts, making avalanches easier to trigger and wider than you'd expect. Wind slabs often form near ridgelines and on the sides of mid-slope terrain features like gullies and ribs. Surface textures like dunes, ripples, or pillows are clues that the wind has been at work. 
  2. Wet Avalanches: Today will be mostly sunny and warm. Natural and human-triggered loose snow avalanches are likely on slopes that face the sun. Roller balls, or groups of snowballs cascading down a slope, are a common precursor to wet avalanche activity. Wet slides are most likely on very steep, rocky, sun-drenched slopes. Although most will be small, some may be big enough to knock you off your feet or bury you in a terrain trap.
  3. Cornices: Large cornices guard the tops of most steep, alpine cirques. Warm temperatures can cause these unpredictable beasts to sag and fail. Limit your time below them and travel far from their edge, where you can easily feel dirt or rocks below your skis or sled. 

Remember, today's spring-like weather is only skin deep. It's not the day to ski or ride the steep terrain you've been eyeing all winter. Thankfully, we can still safely enjoy some all-time late-season snow conditions by sticking to lower slope angles (less than about 35 degrees), watching for obviously wind-loaded slopes, and avoiding the runouts of large avalanche paths.

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