Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
View on map

Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
Open full map
Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions exist. You're most likely to trigger a large avalanche at upper elevations and on shady (NW-N-NE-E facing) middle elevation terrain where weak, sugary snow exists near the base of the snowpack. Slides can be triggered remotely—from flatter terrain below, above, and to the sides of steep slopes.

Avalanche problems

  • Persistent Slabs

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

    Tuesday, near Galena Summit, my ski partners and I remotely triggered avalanches and experienced near constant snowpack collapsing. Some of these collapses traveled hundreds of feet,  cracking slopes like a pane of glass. Yesterday in the Boulders, Ben and I again experienced widespread snowpack collapsing and observed the aftermath of an impressive avalanche cycle in the Smokys.

    You are most likely to trigger a persistent slab avalanche on NW-N-NE-W facing slopes at middle and upper elevation. That said, any slope that had snow on the ground before the recent storm is suspect. For example, yesterday Ben and I got unstable snowpack test scores and experienced snowpack collapsing on a SW-facing slope at middle elevation. The weak layer will vary based on your aspect and elevation but most often presents as facets or a combination of facets above a crust. 

    You can find out whether old snow exists by quickly digging a hole. The old snow will be crumbly, slightly grey, and may contain one or more ice crusts. It could take weeks for the snowpack to adjust to the huge load from this storm. Pay attention to the terrain above you as remotely triggering an avalanche is a very real possibility.  Fortunately, there are still plenty of areas to find great skiing and riding. You can significantly reduce the chances of getting caught in an avalanche by sticking to terrain free from wind effects where the storm snow fell on dirt or bare ground.

    (12/15/2021) Avalanche in wind loaded terrain off the summit of Copper Mountain. NE, 8950'

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Expect to find 2-5 foot thick drifts and slabs in exposed terrain. Wind slabs will be most hazardous where they overlie weak layers (see Problem 1) or slick, icy crusts on more south-facing slopes. However, variations in wind speeds and direction during the storm probably formed slabs that could fail on layers within the storm snow as well. The wind slabs will be thickest, widest, and most widespread at upper elevations, but you may encounter them in middle elevation terrain. 

    Given the 3-5 feet of new snow and strong winds in recent days, the wind slabs are not an easily manageable problem. Wind shifts near the tail-end of this storm as well as fresh thin, wind drifts from today's snowfall will serve to complicate the picture. Thick, older drifts may support your weight in some areas, while thinner or more recent drifts may be touchy in others. While this is a problem worth considering on its own these drifts are far more dangerous where they overlap with the weak layers described in Problem 1. 

    Now is not the time to try to thread the proverbial needle while you're traveling in the mountains. If you see cracks shooting out from your boards or sled, it's time to pay close attention while you head to more sheltered terrain.  

Avalanche Discussion

Here We Go Again

If you're familiar with Central Idaho winters, the message we're sending won't be new. In fact, I'd forgive you if you feel like you've heard a very similar message before—because you have. Early season snows, followed by relatively dry weather and a cold snap preceding our last big storm, formed a weak snowpack riddled with facets and crusts. Toss an epic 3-5' of snow (3-4" SWE) into the mix and the result shouldn't be surprising.

Yesterday, Ben and I climbed high into the Boulder Mountains to glass and snap some photos before the afternoon snow showers arrived. Immediately we picked out several persistent slab avalanches in the Smokys, some of which were visible with the naked eye from over 5 miles away. Later, after sitting down to his computer to take a closer look, Ben described the aftermath as "As widespread of a cycle as I've seen there." Avalanches wrapped hundreds of feet "wall-to-wall" across several shaded, wind-loaded, upper elevation starting zones. With a minimum of 3' of new snow at their disposal, these avalanches were several feet thick. Even more impressive to think about are all the slides that went undetected due to poor visibility during a prolonged, multi-day storm.

In stark contrast to the Smokys, Chris observed only a few large avalanches while glassing the Sawtooths from the Stanley Ranger Station, north to Copper Mountain. Given the snow amounts that fell on a similarly weak, faceted snowpack, avalanches were all but certain. It's possible that these slides occurred earlier in the storm, and subsequent snow masked the crowns and debris. Precipitation rates also slowed in the Sawtooths and Banner in the latter half of the storm as compared to the Smokys, another factor that helps explain the apparent dividing line in avalanche activity late in the storm. 

Although weak snow near the ground, and the attendant persistent slab avalanche problems that arise are nothing new, no two years are the same. Weak layers form, evolve, and heal at different rates depending on aspect, elevation, weather, and mountain range. These patterns take time to uncover and require diligent monitoring. The most obvious pattern we've observed is the prevalence of avalanche activity on slopes that held snow prior to this last major storm. The old snow provides a weak layer and serves to "smooth out" surface roughness like stumps, rocks, and sage providing a bed surface for avalanches to release and slide. As a result, you're most likely to trigger a persistent slab avalanche on shaded middle and upper elevations, but all slopes with old snow near the ground should be suspect. 

Keep an eye on our Observations Page to see what folks are finding. Consider submitting an observation yourself. Tracking and mapping this weak layer is as simple as digging below the recent snow and looking for an ice crust, or weak, crumbly, grey snow near the ground. Better yet, snap a photo of any avalanches you see and listen/look for collapses and cracking in the snow surface. The more data we get, the better we can define the problem, and the easier it is to collectively make safer decisions on where to play.

Regions covered