Avalanche forecast

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Sawtooth Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Monday's wind event moved snow in exposed terrain, depositing it in unusual places. Slopes where recent winds formed drifts or stiffened the snow surface are most suspect today. Underneath these drifts, weak snow buried near the ground continues to pose a threat. To reduce your risk, steer clear of obviously wind-loaded terrain where the snow surface is hard.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Monday's strong NE winds easily moved snow in exposed terrain, forming a fresh crop of soft and hard wind slabs. Some of these relatively thin slabs will likely remain sensitive to triggering today. The slabs formed in unusual places: 

    • On slopes that are typically wind-scoured.
    • Lower in cirques, hundreds of feet below major ridgelines.
    • On the sides of rocky ribs and gullies.

    These slabs will be most sensitive where they are sitting on firm surfaces, like crusts or older hard slabs. Watch for signs of recent wind loading like ripples, dunes, or wave-like patterns. If you are riding in soft snow and it suddenly gets stiff or hard,  it's time to call a time out and carefully evaluate the terrain you're in. Today's snowfall could hide the wind slabs, complicating travel in some areas.

    Keep your head on a swivel while you're out having fun; that slope that usually has your secret stash of powder may have been affected by Monday's wind event. The relatively fresh wind slabs are not a huge hazard on their own, but they are also driving the persistent slab problem discussed below. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–3

    Ben visited an avalanche that released Sunday in the White Cloud Mtns SE of Stanley (photo to right). It broke over 500 feet wide, 4-6 feet deep, and wiped out the majority of the season’s snowpack, covering snowmobile tracks from the previous day. It is unclear if this avalanche failed naturally or was triggered remotely from below. The snowpack isn’t identical in this zone, but similar layers of weak snow exist near the ground.

    In the Boulder Mtns (Galena Summit & Eastern Mountains zone), several 2-3 foot thick slides released naturally Monday on W aspects with thin snowpacks. Monday's unusual NE wind event loaded these slopes that are usually wind-scoured; you might find similar snowpack setups in isolated, exposed terrain in this zone. 

    This is what we're referring to when we talk about unlikely events with high consequences. What are the common threads in the recent persistent slab avalanche activity?

    • Steep: slopes in prime-time avalanche terrain around 35-45 degrees.
    • Wind-loaded: heavily wind-loaded by recent wind events.
    • Alpine flavor: complex terrain with rock ribs, cliff bands, or minor ridges near the avalanche crowns or flanks.

    The consequences of a triggering a destructive, 2-6 foot thick, persistent slab would be severe. Be aware that even if you aren’t in steep terrain yourself, the snow that you are traveling on may be connected to that sort of terrain above you.

Avalanche Discussion

Variety is the spice of life, right? You might have felt like our snowpack was already tricky to manage, but Monday's unusual NE wind event spiced things up a bit. We are dealing with two very different hazards right now:

  1. Despite the lack of fresh snow, strong winds blowing from an unusual direction (NE) were enough to put a large amount of snow “into play” yesterday. These winds quickly built thin, hard slabs where you don't usually see them. 
  2. The persistent weak layers (facets and depth hoar) buried in the lower half of the snowpack aren't ready to go quietly into this good night. Multiple natural avalanches in the Boulder Mountains and an avalanche failing on depth hoar near the ground in the White Clouds are clear indicators that large, destructive avalanches involving this weak snow remain possible.

Dealing with either of these problems individually is challenging in its own right, and the problems overlap on some slopes. The fresh, stiff wind slabs are adding additional weight, stressing the deeply buried weak layers. But that's not all; they are also adding stiffness at the snow surface, an important factor that allows the slab to “communicate” with the weak layers closer to the ground.  

I want to "paint the danger graphic green" and travel carefree in steep, consequential terrain as much as anyone. Unfortunately, we need to balance our thirst for those steep slopes with the lingering—but still real—threat of triggering large slides that could do more than just ruin a fun day. We're not out of the woods yet. 

Regions covered