Lawinenlagebericht

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

You can trigger slides large enough to bury you on many steep slopes. Avalanches will be larger, more destructive, and easier to trigger as you climb elevation bands into terrain affected by the wind. Much larger slides breaking on buried weak layers remain a worrisome possibility and can be triggered from long distances away. Loose snow avalanches will release naturally during periods of direct sun, gaining mass as they race downslope — especially in the steep, rocky Sawtooths.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    2-4 feet of settled snow has fallen in this zone in the past week, with periods of intense winds. You'll observe a wide range of instabilities involving the new snow, depending on the terrain you enter. Avalanches will be most likely in terrain that has been affected by the wind, which is most of the terrain at middle and upper elevations in this zone. 

    Expect stiffened, denser SLABS in more exposed locations near ridgelines — these will be more difficult to identify with lighter, fluffy snow on top. In this same exposed terrain live many large CORNICES, which you should give wide berths when traveling ridgelines. These wind features will serve as effective triggers for avalanches in terrain below them if they fail either naturally or by human triggering. Any one of these types of slides could be large enough to bury you, and can serve as an effective trigger for deeper, more destructive avalanches described below.  

    ADDITIONAL DISCUSSION - LOOSE SNOW: Loose snow avalanches will be easy to trigger on steep slopes. When the sun comes out for the first time since our storm to melt near surface snow, expect these to occur naturally on slopes with direct sun. Becoming more likely throughout the afternoon as skies clear, these slides can run far and fast on slick crusts, gathering a lot of mass as they race downslope even at lower elevations. 

    (2/27/2024)

    This slab avalanche was triggered from 50 ft away on a low-angle ridgeline. It broke widely in wind-drifted snow on a thin layer of facets above a crust. Cracks extended another 100' cross-slope beyond the crown. Smiley Ck, ENE @ 9,100'.

    Photo: Sawtooth Avalanche Center

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    Weak layers in the upper snowpack lie buried underneath this week's snow. Our observations of recent avalanche activity in this zone are limited, thanks to poor visibility. We will know more about these layers once we observe the aftermath of this recent loading event. For today, it's best to assume that these layers exist in most places and that triggering an avalanche on them is a disconcerting possibility. The photo at right/above shows a large persistent slab that failed near Baker Creek, in a neighboring forecast zone. 

    Avalanches that fail on persistent weak layers behave in ways that surprise even experienced users. These slides will break wide, wrapping around entire bowls and cirques. You can trigger these avalanches from long distances away from steeper slopes, including from flat terrain below large avalanche paths. Any of the storm snow avalanches described below can trigger these much larger slides. 

    Deeper weak layers are buried underneath the very dense, 4-5 foot thick slabs that formed from snow in February. Triggering an avalanche on these layers is much less likely, but any slide that breaks on them will be massive. Smaller natural and human-triggered avalanches can step down to these deeper weak layers. Slides that break on these layers can wipe out swaths of mature timber and will be unsurvivable. 

    This photo shows several large to very large avalanches that failed above the Baker Creek drainage, likely overnight Friday into Saturday. The crowns span hundreds of feet of terrain, and are an estimated 3-5 feet deep in places. Getting caught in an avalanche like this and being dragged through the trees below would likely be unsurvivable. This slope faces E-SE at 9,700'.

    Photo: Ben VandenBos

Avalanche Discussion

Multiple large human-triggered and many natural persistent slab avalanches have run in recent days. Triggering slides similar to these remains a worrisome possibility today. Each of these gives us data points to keep in mind when heading into the mountains:

  • Skiers remotely triggered a large persistent slab avalanche in out-of-bounds terrain near Baldy yesterday. This slide broke 700' wide in terrain that had already been skied several times on a E aspect near 8100', was 4-8' deep in spots, and ran 1500' into a creek below. Multiple skiers had descended this slope before this slide occurred, not receiving any warning signs. This slide occurred in terrain outside the ski area boundary commonly called Sunspot Bowl. Out-of-bounds (OB) terrain, even in close proximity to the resort, is consequential and not mitigated for avalanche hazards by ski patrol. Any skier or boarder choosing to enter OB terrain should treat it as entering the backcountry and have the appropriate avalanche gear and training. While not receiving any obvious indicators of instability, slides like these remain a worrisome possibility.
  • Sun Valley Heli remotely triggered a large persistent slab avalanche from an adjacent slope yesterday, as well as noting multiple other D2 slides that ran naturally. Each of these slides ran beneath the new snow,  proving our newest weak layer to be reactive. SVHS also intentionally triggered a couple of large cornices above complex NE-facing terrain near 9800'. These failing cornices triggered large avalanches on the slopes they impacted below, which ran on facets near the base of the snowpack. This reminds us to be mindful of cornices both in the terrain we are traveling through and above us.
  • Ben observed several large to very large naturally occurring persistent slab avalanches in the Boulder and Smoky Mountains that ran during the past storm. Scott spotted more of these in the Sawtooths yesterday. It is more than likely that many more similar slides have occurred throughout our forecast area. 

This week will provide ample opportunities for high-quality skiing and riding. This being said, knowing that avalanches like these remain a worrisome possibility should be driving your trip planning and decision-making headed out into the hills. Luckily enjoying soft powder flowing over the hood, or snow in your face does not require entering avalanche terrain. 

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