Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

The likelihood of small wet slides—both natural and human-triggered—will increase as the day warms up. There is a small chance of triggering a slab avalanche on upper elevation slopes facing NE-N-NW. Use caution on slopes with evidence of wind drifted snow.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Sunshine and warming temperatures today will increase the likelihood of both natural and triggered wet slides. The 4-6" of snow that fell last week is sitting atop slick crusts—an excellent recipe for wet snow avalanches once you add direct sun. You could trigger a wet avalanche on steep slopes that face the sun (S-E-W). Although likely to be small, these slides can travel quickly on the slick surfaces beneath them. Natural wet sluffs could occur as the day heats up—so pay attention to the terrain that's above you.

    ADDITIONAL DISCUSSION:There are two less likely problems to keep in mind today: 

    • There's a small chance of triggering a persistent slab avalanche on a shady slope (NE-N-NW) at upper elevations. Our direct observations on this layer have been limited, but with the lack of recent loading, we expect triggering a persistent slab to have become unlikely. Upcoming storms—tonight/tomorow and especially Monday night into Tuesday—could bring this problem back to the forefront.
    • Yesterday, I observed a number of fresh wind drifts at upper elevations, but these were small and didn't seem particularly sensitive. These wind slabs seem to be less problematic than in our southern zones, but use caution on slopes with evidence of fresh drifting.

Avalanche Discussion

Conditions aren't scary out there, or particularly dangerous, but there are enough smaller problems that you need to keep your head on a swivel. If I had one word to describe the avalanche conditions, I wouldn't use LOW or MODERATE...I'd use "annoying". 

Normally, wind slabs and wet slides are two of the more predictable avalanche problems we deal with. The elephants in the room are persistent weak layers that we've formed during the past two months of dry weather—facets, crusts + facets, and surface hoar. We've seen a few avalanches where wind slabs have broken thicker and wider than expected (example) when they fail on these weak layers. In the Banner Summit zone, the wet storm at the very end of February triggered a cycle of persistent slab avalanches breaking on facets, crusts, and surface hoar. 

The prolonged dry spell produced several weak layers, but the wind, sun, and warm temps also produced a high degree of variability. Persistent weak layers + variability leads = unpredictability. When conditions are more unpredictable, it leads to a degree of uncertainty that makes forecasters unhappy. We don't like rolling the dice. Despite the MODERATE danger and relatively low likelihood of triggering a large avalanche, many avalanche professionals remain wary of some slopes. Those of us at the avalanche center are tending to avoid steep slopes at upper elevations that are shaded (more likely to harbor weak layers) and wind loaded (adding more load to the weak layers).  

Catch up on what happened this past week in Ethan's latest Weekend Update.

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