Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

You're most likely to trigger a large avalanche in areas where the wind has stiffened the snow surface or built thick drifts. You may be able to trigger these avalanches remotely—from flat terrain below, above, and to the sides of steep slopes.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2

    Yesterday's W and NW winds caused natural slab avalanches to release near exposed ridgelines. Recently formed 1-4 foot thick slabs sit atop various weak layers (facets, surface hoar, crusts, and crust + facet combinations). 

    The widespread nature of the weak layers means avalanches may be triggered on many aspects. The odds you trigger a slide are greatest where wind formed drifts or stiffened the snow surface. Avalanches are less likely but possible on steep slopes more sheltered from the wind. 

    Signs of recent wind loading include cornices, dunes, or drifts. Snowpack collapsing or whumpfing means you've found a sensitive slab. Persistent Slabs can release in surprising ways, break wider than expected, and release above or hundreds of feet away from where they are triggered. Remotely triggering an avalanche from flat terrain below steep slopes remains a concern. Keep a close eye on your partner and the terrain above you.

    (12/15/2024) This large, natural avalanche released on Saturday or Sunday in wind-loaded terrain in the Beaver Ck drainage in the western Smoky Mtns, in the forecast zone to the south of the Banner Summit zone. E aspect near 10000'. 

    Photo: Ben VandenBos

Avalanche Discussion

If you got out to enjoy some fresh air yesterday, you may have noticed the wind lifting large plumes of snow from ridgelines and high peaks (Pioneers, W. Smokys). Yesterday afternoon and evening, wind speeds blew strong to extreme from the W and NW. An observer in the Western Smokys shared this photo of a natural slab avalanche caused by wind loading. The persistent slabs described above have two primary ingredients: buried weak layers and a slab. Put that combination into avalanche terrain, and you've got a problem. Since the end of our recent storm, we've found plenty of weak snow, but some slopes lacked a stiff enough slab. Yesterday's wind event changed that in many areas. 

Today, you can drastically reduce your risk of triggering a large avalanche by looking for and avoiding areas with a stiff slab near the snow's surface. Actively seeking out softer snow is safer and more enjoyable but doesn't completely eliminate your risk. Given the sensitive weak layers we're dealing with even deceptively soft slabs have the potential to release in steep terrain. The consequence of these smaller slides increases on slopes with terrain traps like gullies, cliffs, or thick trees. 

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