Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions exist, especially on wind loaded slopes. The wind has transported the copious amounts of new snow into touchy drifts and slabs—you're likely to find these in upper elevation, wind-exposed terrain. The snowfall is also adding weight to buried weak layers, and it's possible to trigger a very large avalanche 2-4 feet deep—even on wind-sheltered slopes. Expect the avalanche danger to rise overnight as the next significant round of snowfall hits our area.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Observations yesterday indicated that wind slabs were probably more of a concern than the persistent slab problem, and they've been bumped to the top of the list today. Yesterday in the neighboring Banner Summit zone, I observed optimal wind speeds for transporting the copious amounts of low-density new snow. I found both stiff and soft drifts of windblown snow, and these cracked easily under my weight (see photo). I'd expect these to be less touchy today, but you'll want to avoid any slope with wind-drifted snow. This zone received enough new snow that these wind slabs could produce a large enough avalanche to bury you, and there is the possibility of a slide stepping down into the persistent weak layers described below.

  • Persistent Slabs

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

    Following the New Year storm, this zone received nearly continuous light snowfall starting January 4th. This snow has added up, and the persistent weak layers we've discussed all year are becoming deeply buried—from 2.5 to more than 4 feet deep in most portions of this zone. This means two things: persistent slab avalanches are becoming harder to trigger; but if a slide releases, it's likely to be very large. We're trending towards a dreaded low probability, high consequence scenario—or LPHC as acronym lovers call it.

    It's not entirely clear how these buried weak layers will respond to the loading from yesterday's snowfall, tonight's storm, and the slow trickle of snowfall over the coming week. Go back to the basics: we have persistent weak layers, and they are getting loaded with significant amounts of new and windblown snow. Until we have more information, this problem is too much of a high-stakes gamble to mess with. The best—and really only—way to manage this problem is by choosing lower-angled slopes.

Avalanche Discussion

Snowpack conditions within our forecast area have begun to diverge. Following the New Year storm, a nearly constant trickle of snow has fallen in our northern and western mountain ranges. Additionally, yesterday's storm, tonight's, and the snowfall this week continue to favor these same areas—the Western Smokys, Sawtooths, Banner Summit, and to some extent, the Soldiers. For the first part of the winter, we had fairly uniform conditions across the forecast area. That situation has changed, and will continue to change, over the coming week.

In our northern and western mountains, the persistent weak layers we've been talking about all winter are becoming quite deeply buried. The surface hoar and depth hoar from early in the winter are now buried beneath 3-4 feet of snow. A newer weak layer that formed prior to the New Year's storm is 2-3 feet deep. With another 12-16 inches of new snow in the forecast tonight, these weak layers continue to get pushed further underfoot and are becoming harder to trigger. But it should come as no surprise that triggering an avalanche 2-4 feet thick is no joking matter. It's also becoming more difficult to predict what these deep weak layers will do under the slow but constant loading we're currently experiencing.

The Galena Summit area, our Eastern Mountains, and especially the Wood River Valley have received overall snowfall since the start of the New Year. These areas have a snowpack that's a bit thinner with more prominent persistent weak layers but have received less recent loading to aggravate them. These weak layers are 1-3 feet deep and are more easily impacted by the weight of a rider. Will these areas receive enough snow over the coming days to make these layers wake up? Time will tell.

But our area does have one thing in common. Even if it comes in different forms, there's a high degree of uncertainty in how our snowpack will react to the extended storm cycle we're experiencing. Uncertainty means building more margin for error into our terrain choices. The best approach—and the one I plan to take—is to sit back, enjoy some fantastic low-angle powder riding, and see what shakes out.

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