Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
View on map

Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
Open full map
Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Conditions are dangerous. Expect to trigger large, 1-3 foot thick avalanches where the wind has drifted snow or stiffened the snow surface. Similar slides are possible in terrain more sheltered from the wind.

Avalanche problems

  • Wind Slabs

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

    Expect to find sensitive slabs in both obviously wind-loaded and more sheltered terrain. Yesterday, Ben observed a large avalanche on the north side of Copper Mtn near Banner Summit (photo above/right). You could trigger similar avalanches today.

    Slabs will be thicker, wider, and more dangerous at windier, upper elevations. Look for them near ridgelines and along mid-slope terrain features like ribs and gullies. Stiff slabs may extend into wind-exposed middle elevation terrain. Some wind slabs formed over weak snow (facets, surface hoar, crusts), which may make them more sensitive to triggering and could cause them to break wider than expected.

    Snowpack collapsing or cracks shooting from your skis or sled are obvious signs of instability. Ample low density snowfall and shifting wind may mask the usual clues that the wind has been at work. This may make it difficult to identify a recently wind loaded slope from a distance. Even subtle wind affect over the past ten days may be enough to stiffen the snow and increase your odds of triggering a slide.

     

    (2/28/2023) This large avalanche was observed on a N aspect of Copper Mountain near Banner Summit. The crown extends into terrain that is mostly sheltered from the wind.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Recent snowfall is overloading layers of weak snow in the upper 3 feet of the snowpack—sugary facets, crusts, or crust + facet combinations—on some slopes. You may be able to trigger slab avalanches in protected terrain. You could trigger these avalanches remotely, from gentle terrain above, below, or to the sides of steep slopes.   

    This problem is most likely in middle and upper elevation terrain because more snow fell there in the past few days. The weak layers’ appearance and “behavior” will change over short distances; minor differences in aspect, elevation, and exposure to the wind created variability in the crusts and facets underneath the newer snow. You’re most likely to find trouble on slopes steeper than 35 degrees.  

    Assume this problem exists until proven otherwise. You may experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability. Snowpits and snow stability tests are of limited use due to the weak layer variability over short distances. You can reduce your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if you are caught in an avalanche. These slides may break wider than expected or higher on the slope above you. The first skier or rider may not trigger an avalanche on an unstable slope. Do not assume tracks mean a slope is safe. 

    (2/28/2023) NE face of Copper Mountain at 8,400'. This photo shows a portion of the crown of an avalanche that appeared to be remotely triggered by a skier from above. The avalanche was triggered in slightly more wind-affected terrain, though this crown in sheltered terrain points to the potential for encountering avalanche problems outside of areas that are obviously affected by the wind.

Avalanche Discussion

Steering clear of wind-loaded avalanche terrain is the best way to reduce your risk of triggering a large avalanche, but it's far from the whole story. Wind-loaded slopes harbor recently formed drifts and slabs. These slabs will be dangerous in their own right, thanks to the combination of several inches of new snow, wind, and the weak layers on which they formed, but they also add weight to a host of weak layers in the upper 3' of the snowpack. So far, the majority of the slides we've seen have initiated in wind-loaded terrain, but this is starting to change. Slabs of snow are beginning to overwhelm weak layers in terrain that lacks an obvious wind load. 

We added a persistent slab problem in the Sawtooth and Western Smoky Zone yesterday. This zone has received the most recent snow and has the thickest slab. The Banner Summit Zone is not far behind and I added a persistent slab problem there this morning. Honorable mentions go out to the White Clouds, Smokys, Soldiers, and the mountains surrounding Galena Summit and Dollarhide Summit. These areas may be slightly behind, but not by much. 

While wind-loaded slopes are obviously dangerous today, identifying a wind-loaded slope from a distance could be challenging. If you are planning to head to any of the abovementioned areas, know that it may no longer require an obvious wind load to be dangerous. Many slopes may be teetering on the edge. Today is a good day to choose conservative terrain, keep your slope angles low, and anticipate the possibility of triggering a slide from below, above, or to the sides of a steep slope. Let's take a step back today and see how it all shakes out.

Regions covered