Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Thu
Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Highlights

Large avalanches are unlikely. The highest chance of triggering large slides is on very steep, rocky, wind-affected slopes. You might find small, recently-formed wind drifts in extreme terrain. 

Avalanche problems

  • Persistent Slabs

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

    Triggering a persistent slab avalanche is unlikely but not impossible. Deeply buried, persistent weak layers (facets, facets and crusts, isolated surface hoar) exist on nearly all slopes. Know that they are under your feet or sled. Warm and dry conditions last week finally gave these weak layers some time to rest, but they did not magically go away.

    You're most likely to find trouble on very steep (approaching 40 degrees), rocky, wind-affected slopes. Terrain like this is most common at upper elevations. Because these weak layers are deeply buried, any slide that fails on them will be large and destructive.

    ADDITIONAL DISCUSSION: Isolated wind slabs formed in "extreme" terrain in the past couple of days. Though small, these slabs could be sensitive to your weight. Calm, clear weather today could produce some small, sun-induced loose snow avalanches in very steep, rocky terrain, most likely on E-S-W aspects. Think about the consequences of being caught in even a small slide before committing to serious, exposed terrain. 

    (3/5/2021) Persistent weak layers in the Banner Summit zone are unlikely to produce avalanches - but they're still there. Here, a layer of surface hoar 3' down didn't fail during a snowpack test, but sheared when the block was pried out of the column. N, 8400'.

Avalanche Discussion

LIMITATIONS OF THE AVALANCHE DANGER SCALE

The avalanche danger scale is neither precise nor linear. For the sake of discussion, let's say LOW danger is represented by a mythical, numerical rating of 1-10, and MODERATE danger is represented by 10-100. The fictitious numbers demonstrate that we can have large differences in danger within the same danger rating; Zone X could be 10 times more dangerous than another zone with the same rating. Today, all our zones are rated LOW. Are there differences between the zones? Heck yes! Here's a quick rundown:

  • Soldier & Wood River Valley Mountains: This zone has seen the least snowfall in the past couple of weeks and has the most stable snowpack throughout the bulk of the zone. The mountains near Dollarhide Summit are the exception; there, the snowpack looks more like it does around Baker Creek in the Galena Summit & Eastern Mountains Zone. I'll give this zone—excluding Dollarhide—a 2. 
  • Banner Summit: The Banner Summit area picked up 3-6 inches of snow earlier this week, but that wasn't enough of a new load to impact the deeply buried weak layers. With light winds accompanying the snowfall, fresh wind slabs are few and far between. Banner also gets a 2. 
  • Sawtooth & Western Smoky Mountains: You should expect to find some fresh wind slabs in extreme terrain in this zone. The recent snowfall was not enough of a load to impact the deeply buried weak layers, so triggering large slabs is unlikely. The combination of mostly clear skies and light winds will probably allow the sun to produce some small, natural, loose snow avalanche activity. I'll give this zone a 4. 
  • Galena Summit & Eastern Mountains: The snowpack in this zone still gives the SAC forecasters and local professionals pause. We're generally avoiding large, consequential avalanche terrain—picture big, open bowls peppered with rocks in the alpine terrain of the Boulder, White Cloud, and Pioneer Mountains—because the snowpack structure is still so creepy looking. We don't trust it. Yes, triggering large slab avalanches is unlikely. But, if I got the call that an avalanche accident occurred today, I'd expect it to be in alpine terrain in this zone. I'll give it an 8.

With this exercise, I'm attempting to shed some light on how all LOW danger is not created equal. The green LOW rating does not automatically mean "send it, and go anywhere you want without worrying about avalanches." I think the alpine terrain in the Galena Summit & Eastern Mountains zone is a much more dangerous place to be today than the rest of the terrain in our forecast area—about 2-4 times more dangerous than the other zones.  Remember: the danger rating and avalanche forecast are meant to give you baseline information to use in your travels, but YOU get to make the decision whether riding or skiing specific terrain is a good idea or not.

 

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