Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Triggering an avalanche large enough to bury you is possible today. Smaller pockets of wind-drifted snow near ridgelines will be reactive to your weight. Much larger avalanches involving very dense hard slabs can break 2-4 feet beneath the snow surface and send the majority of the season's snowpack downslope. Both types can be triggered from long distances away from the slope that avalanches. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3

    Triggering large to very large avalanches here is a disconcerting possibility. These slides come in two flavors:

    • Weak snow from December forms the base of the snowpack and has produced dozens of avalanches large enough to turn your car into scrap metal. A very dense slab rests uncomfortably on top of this weak snow. This slab makes triggering one of these avalanches much more difficult, but the resulting slide would be destructive and likely unsurvivable. The first sign of instability on this weak layer will be the very large avalanche you trigger. The most likely terrain for making one of these beasts is steep, rocky, wind-affected terrain where the snowpack has thinner spots that give you access to the weak layer. 
    • Several weak layers exist in the upper 12-18 inches of the snowpack. These layers are highly variable. On some slopes they are well bonded, while on others they are producing large avalanches. You may find good stability on one slope and then trigger an avalanche when you change to a nearby slope. Cracks shooting out from your skis or machine are a clear sign you've found an unstable slab. The human-triggered slides that have failed on this layer have involved crust+facet combinations and have been triggered from a distance (remotely). 

    Persistent Slab avalanches behave in ways that catch experienced users off guard. You can trigger them from flat or low-angle terrain long distances away from steep slopes, and they can break far above you. Dozens of skiers or riders can ski/cross/highmark large slopes before a very avalanche releases. 

  • Wind Slabs

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

    Sustained strong winds began 3 days ago. While yesterday's storm significantly underproduced precipitation, it delivered on wind. While there was not significant amounts of new snow available, strong wind transport stripping ridgelines close to bare were observed, with wind gusts reaching 105mph at the Soldier Mountain weather station! While this problem will be more dangerous where more snow fell, such as in the Soldiers, expect the strong winds to have built small wind slabs throughout upper and middle elevation terrain. The Wood River Valley Mountains will have significantly less of these issues with less snowfall, and wind. 

    At upper and middle elevations, you'll find reactive these slabs as well as loose snow avalanches that run fast and far on weak, slick surfaces. These could be large enough to bury you, and at their smallest, largest enough to take you for a ride down through consequential terrain like cliffs and trees. Rippled snow surfaces, dunes, pillows are all signs that the wind has been at work. The ongoing light-density snowfall and wind may make it harder to identify where wind slabs exist. Importantly, natural and triggered slides involving the new snow can trigger the much larger, more destructive persistent slabs described below. 

Avalanche Discussion

Yesterday's storm under-produced snow in this zone, but not on wind. The weather station on Soldier Mountain recorded winds gusts up to 105mph, which loaded a variety of weak surfaces from surface hoar to facets to crusts. While these slabs will be quite small in the Wood River Valley Mountains, in areas where more snow fell like the Soldiers this new / old snow interface is likely to produce avalanches, albeit small. Near Copper Mountain where more snow fell, Ben observed multiple natural storm slabs running on the slick interface last night. At least one of these stepped down to a deeper weak layer, and he remotely triggered another from a distance. This new weak layer, now 3-6 inches in the snowpack in this zone, is just our newest interface to trigger at the top of the stack of slabs and weak layers that currently make up our snowpack. The sustained wind also loaded start zones that typically don't get loaded all the way down to roadway levels.

And this is just what lies near the surface. What does the rest of our slab-weak layer-slab-weak layer (etc.) stack — or snowpack — look like? Let's take a peek, from the top down:

Underneath our new storm snow and weak snow beneath it (2/25 weak layer) described above, we have roughly 2 feet of settled, dense snow from our storms in February. Below this slab, a variety of weak surfaces formed in different locations, from rain crusts, to sun crusts, to facets that developed at the end of January (2/1 weak layer). A smattering of natural and human-triggered avalanches involving this layer clearly indicate that it is capable of making avalanches, but stability varies significantly from slope to slope. On some slopes, you'll find a strong bond at this interface, while neighboring slopes may be harboring an unstable slab+weak layer combination. Avalanches that fail on this layer will break widely and will be plenty large to bury you. 

Closer to the bottom of the snowpack, we have a thicker layer of rotten, faceted snow that sat out during our December drought (1/6 weak layer) and has a dense, thick slab overlying it. While this weak snow is so deeply buried it is unlikely to trigger avalanches on, know that a slide running on this layer would almost certainly be unsurvivable with 2-4ft of snow moving downhill with you. 

Our slab-weak layer-slab-weak layer stack here in Idaho can create some excellent days skiing and riding out in the mountains — with cold temperatures and just a bit of sun, today will certainly be one of them. With that said, it is just as important to keep in mind what lies below the soft turns as it is to seek them out. The depth of our snowpack is increasing, as is the complexity of it. The intention of the Forecast is to provide you with the information to be able to make informed decisions that keep you safe in the mountains based on information you read here and observations you take in the field. Having a hypothesis of what the snowpack may look like from the forecast, heading into the field, and taking observations on your hypothesis matched up to actual conditions is how we make informed decisions in the hills, and grow as mountain travelers. Enjoy the soft snow, be safe, and continue to have a curious mindset when you head out today.

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