Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
View on map

Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You could trigger large avalanches in steep terrain, especially in areas with stiffer, wind-deposited snow. Avalanches are less likely—but still possible—in terrain sheltered from the wind. Avalanches may be triggered remotely—from areas below, above, and to the sides of steep slopes. Small, loose snow avalanches are possible in very steep terrain.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Triggering a large, 1.5-2.5' thick avalanche is most likely on slopes with the following characteristics:

    • Slopes steeper than about 35 degrees.
    • Well-developed facets in the middle of the snowpack.
    • Where wind has stiffened the snow in the upper part of the snowpack and/or formed hard drifts on the surface. 
    • Slopes that face W/NW-NW-N-NE-E-SE. These aspects are where the majority of our recent avalanche activity has occurred and harbors the ugliest underlying snowpack structure. 

    Because the weak layer is more deeply buried around Banner Summit, it's getting more difficult to trigger avalanches. Unstable slopes may not give you obvious "red-flags" like snowpack collapsing, shooting cracks, or poor instability test scores. Unfortunately, when you find the wrong spot, the resulting slide will be large and dangerous. 

    There's a real chance of remotely triggering slides—from areas below, above, and to the sides of steep slopes. Be aware of the terrain you are in and the terrain above you.

    ADDITIONAL DISCUSSIONSince Wednesday night, up to 10" of new snow fell in this zone with very little wind. Loose snow avalanches are possible on all aspects in very steep terrain. These slides may be triggered by you, or occur naturally as the sun warms a slope. 

    (12/23/2020) Large avalanche that released in the southern end of the Banner Summit zone. It broke hundreds of feet wide on weak facets buried in mid-December.

Avalanche Discussion

If this season's snowpack could make a New Year's resolution to be less terrible, we'd all be better off. Unfortunately, once a persistent weak layer of this caliber is buried we're going to have to live with it, in some form or another, for the remainder of the winter. 

Since burial in mid-December, this stack of weak facets has treated us to a wide array of avalanche activity–both natural and human-triggered. Do me a favor and click here to view an image of notable avalanche activity this season. You'll notice one thing right off the bat. The majority of this season's slides have occurred in the western and northern reaches of our forecast area; roughly on a line from Baker Creek north to Banner Summit. This activity coincides with the heaviest snowfall since mid-December. To view an interactive map of this data, click here. 

It's important to remember that the foundation of the snowpack is similar across all of our forecast area from the Wood River Valley and the Soldiers up to Galena Pass and on into the Sawtooths and eventually Banner Summit. This video from Wednesday illustrates this point. The lack of avalanche activity in the southern and eastern portions of our forecast area is not because it lacks weak snow, but because the overlying slab is still in its infancy. This picture may change drastically next week as a series of storms impact central Idaho. 

If we can learn from what we saw up north, we should expect very touchy conditions if the drier portions of the forecast area receive even modest snowfall. In those locations further north where the overlying slab is already thicker slides may be harder to trigger or potentially less numerous, but much larger. This video from yesterday in the mountains west of Smiley Creek touches on this point.  It's safe to say that we'll see increasing avalanche danger this week as storms take aim at our region. Watch the forecast closely, as the effect of these storms is likely to be quite different where the snowpack is deeper in our northern and western zones than where it's still relatively shallow. 

While the snowpack can't wipe the slate clean (just yet), we can. If you are a resolution type of person, take some time to reflect on how you've been traveling. Remember that "good luck breeds bad habits". Did you simply dust off your pack and head into the mountains? Or did you take the time to think of how you can improve your safety margin as a backcountry traveler?

Regions covered