Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Wed
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 6 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Conditions are tricky. You can trigger large avalanches on some wind-drifted and sheltered steep slopes. You may or may not see signs of danger before triggering a slide. You could trigger avalanches remotely—from flat terrain below, above, and to the sides of steep slopes. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–2.5

    What and where is it?

    • The slabs: February storms formed 1-3 foot thick slabs on many slopes. The slabs are largest, stiffer, and most widespread in wind-loaded middle and upper elevation terrain.  However, last week's strong wind built slabs on more middle and lower elevation slopes than usual, and snow has consolidated into slabs on most wind-sheltered slopes.
    • The weak layers: The slabs overlie multiple weak layers (sugary facets, surface hoar, or crust + facet combinations) on many slopes, including sunnier aspects. The weak layers remain most suspect on slopes facing the northern half of the compass (NW-N-NE-E). 

    This diagram shows the spatial pattern of recent avalanche activity. Many recent avalanches were hundreds of feet wide, pulled into gentle terrain, and / or were remotely triggered.  

    How can we recognize and manage this problem?  Determining whether a given slope is safe to shred or waiting for a trigger—you— is challenging. Due to the variable distribution and character of both the slabs and weak layers, stability can change quickly over short distances. You may or may not observe snowpack cracking and collapsing, clear signs of unstable conditions, before triggering a slide. 

    Unfortunately, the only surefire way to avoid trouble is to give avalanche terrain a wide berth. You can stack the odds in your favor by steering clear of steep, wind-loaded slopes, especially those facing away from the afternoon sun (NW-N-NE-E aspects). Watch for dunes, waves, and textured surfaces created by wind. Wind-driven snow and slabs feel stiff. Recognize that you could trigger avalanches on slopes above, below, and to the sides of where you are riding or skiing. 

    Additional Discussion - New Snow issues: The little bit of fresh snowfall and wind-drifted snow may not bond well to the old snow surface. You may see small, sun-induced loose snow slides (sluffs) or thin wind slabs where more than a few inches of new snow fell. Be alert for instabilities involving the new snow. While these slides should be small and isolated, they could trigger the larger, far more dangerous Persistent Slab avalanches described above. 

Avalanche Discussion

Over 100 avalanches (natural and remotely triggered) released last Wednesday-Friday. The persistent weak layers responsible for the carnage (watch the video above) are well-developed and slow to strengthen. The good news:

  • We are seeing and receiving fewer reports of obvious signs of instability (snowpack cracking and collapsing) each day.
  • The likelihood of triggering an avalanche is declining, and many slopes are now safe to ski and ride.

The bad news:

  • Accurately determining which slopes are safe is difficult due to the spatial variability of both the slabs and weak layers. Yesterday, observers reported significant collapsing in the White Cloud Mtns and wisely decided to change plans and avoid avalanche terrain. Thanks for the excellent, simple Observation! Their report highlights both sound decision-making and the variable nature of this problem; stability is good in some drainages/on some slopes and poor in some areas. 
  • Buried surface hoar appears to be the culprit in some of the recent activity. Surface hoar is a notoriously unpredictable weak layer. 
  • Triggering avalanches is possible on slopes that are usually stable: wind-sheltered slopes between 7500- 9000'.
  • If you trigger a slide, it could break large and wide. 

Be ready to pivot to a safer, more conservative plan B if you see signs of instability. Think about the consequences of triggering an avalanche before committing to riding or skiing steep slopes. If the avalanche would drag you through trees or carry you into in a creek bottom or gully where debris could pile up, you need to determine if it's worth the risk. 

Régions couvertes