Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

You can easily trigger large avalanches from a distance that fail in surprising ways on most steep slopes today. Avalanches will be larger and more destructive as you gain elevation and move into wind-affected terrain. Skiers and riders remotely triggered large to very large avalanches from hundreds to thousands of feet away each of the past four days, and similar slides are likely again today. Our snowpack is complex, and unstable — build in wide safety margins where you choose to travel.

Avalanche problems

  • Persistent Slabs

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

    Recent storms built a thick slab of snow on top of a widespread weak layer. Warm temperatures have allowed this slab to settle and consolidate. Skiers and riders remotely triggered large to very large avalanches involving this snow from hundreds to thousands of feet away on each of the past three days (photo at right/above). Large avalanches will be easy to trigger again today. Expect to be able to trigger them from a distance away and to see them break wide and fail in unusual locations.

    In sheltered terrain, expect to find slabs that are 1-2.5 feet thick. In terrain that has been affected by the wind, you'll find very dense, 2-5 foot thick slabs. Under these slabs, you'll find our primary weak layer of concern — surface hoar and/or facets on shaded slopes and a melt-freeze crust with facets on top on sunny slopes. Large natural and human-triggered avalanches failing on this weak snow have been observed on most aspects.

    Not enough weak snow for you? Further down in the snowpack, near the ground, another weak layer exists. Avalanches that step down to this layer of snow will send the entire season's snowpack rocketing downslope. This basal weak layer (located at the base of the snowpack) exists on upper elevation slopes and shaded middle elevation slopes. Avalanches that break down into this snow are likely to be unsurvivable. 

    This photo shows several large avalanches that were remotely-triggered by riders in the Beaver Creek drainage. The furthest away slide is over 800 feet wide, and failed a half mile from where the avalanches were triggered, out of sight on the right side of the photo.

  • Wind Slabs

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

    If you choose to pick your way through the low and mid-elevation terrain where the persistent slab lives — which is most slopes — you may find other smaller avalanche issues that involve the most recent snow. The main takeaway here is that if triggered, any of these issues can step-down to the persistent slab described above to create a much larger, more destructive slide. In exposed terrain, expect to find some small wind slabs that may be sensitive to your weight. Loose snow sluffs can be triggered where snow surfaces remain dry in cooler, higher locations, while warm moist snow on the surface may be able to create wet loose slides. While each of these has its consequences, your main concern should be the increased likelihood of triggering a persistent slab where these problems exist.

Avalanche Discussion

DANGEROUS EVEN FROM A DISTANCE

Walking out the door today, focus on the fact that you will find a complex, unstable, and unwelcoming snowpack in the mountains — one that is capable of producing surprising and very large avalanches from a distance away. The snowpack has been under constant stress for the past 10 days. It hasn't just been recently loaded, but doubled in depth in many places. There was a 36-hour long extreme wind event, a cold snap to warming trend that swung temperatures between -40 to 40F, and 3 distinct avalanche cycles that brought us near-historic slides both natural and human-triggered. In each of the past four days, skiers and riders have remotely triggered large to very large avalanches. One of these slides was triggered from over a half mile away and produced an avalanche that could damage your house. 

Where are you going to get in trouble today? The Banner Summit Zone has a lot of smaller, less obvious avalanche terrain at lower and middle elevations. Here, you'll find many short avalanche paths that end in terrain traps. Imagine sharp road cuts, narrow gullies, and creek bottoms with steep slopes above them. While this terrain can be friendly when stability is good, it is deceptively hazardous on days like today. In recent days, we've seen many avalanches failing in this type of terrain, piling up debris deeply below. As you gain elevation you'll find increasingly thick slabs that have been stiffened by the wind. You can make very large avalanches here, the type that break hundreds to thousands of feet wide. Be suspicious of steep, snow-covered slopes at all elevations.

Where we choose to place ourselves in relation to avalanche terrain is the number one thing we can control in the mountains. We usually manage these hazards by giving avalanche paths some distance. Today I'm telling you that things are dangerous even from a distance. If you choose to head out into the mountains today, remember that you don't only have to manage the terrain that you are traveling immediately through, but the large paths above, below, and adjacent to you. Slides will break in surprising locations, can extend back into low angle terrain, and may span wider than you might imagine. Being aware of traffic below you and other parties traveling in your drainage will be crucial to trying to manage these large, destructive, avalanches that have proven to be easily triggered remotely. Today is the type of day that a slip in your attention to terrain could prove disastrous. 

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