Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Several layers of weak snow are buried in the snowpack. The recent storm added weight to these weak layers, particularly in areas where winds built drifts and slabs. As the likelihood of triggering an avalanche on these layers gradually decreases, the possibility remains. Make your terrain selection accordingly and be alert to the consequences of being caught in a slide where you are traveling. You can significantly decrease your likelihood of triggering an avalanche by sticking to lower-angle terrain that is sheltered from the wind. 

Avalanche problems

  • Persistent Slabs

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

    As we move away from the loading event that brought improved skiing and riding conditions to our area, we focus our attention on the persistent weak layers that are buried in the snowpack. There are two broad categories in this zone:

    1. Last week's storm buried a variable snow surface. We observed a few avalanches that failed on this interface during the storm (photo at right). Warm temperatures and direct sunshine today will help this storm snow to settle into a denser slab, which will continue to make triggering an avalanche involving this snow possible today. It will take some time to see how this interface will behave, it is worth having it in your mind as you travel.
    2. Weak layers that formed at the end of January and during the month of February are now buried 2-4' deep. These layers have produced avalanches across most of our forecast area in the past two weeks (Dollarhide, Galena Summit, Smiley Creek, Beaver Creek, Sawtooths, Banner Summit). The pattern of activity outlined by these avalanches points to these layers being most unstable on slopes that face the sun, where they are accompanied by crusts, but unstable surface hoar has also been observed in this zone. 

    As their name implies, persistent weak layers tend to stick around for quite a long time. As days pass without loading, the snowpack is getting some time to rest, which will gradually decrease the likelihood of triggering an avalanche on these weak layers. However, the possibility of triggering a slide here will be on the table for some time to come. If you choose to enter avalanche terrain, be alert that at least one of these weak layers almost certainly exists in the snowpack underneath you. Even as the danger decreases we still advise cautious and conservative terrain selection. Be alert to the consequence of being caught in a large avalanche in the terrain you are recreating in.

    ADDITIONAL DISCUSSION:Today's warm temperatures and bright sunshine are a perfect combination for loose snow avalanches. Expect to see sluffing of the new snow as the surface warms up, especially on steep, rocky slopes. These sluffs could be dangerous on their own or could trigger larger slab avalanches as they travel downhill.

    (2/26/2021) Small natural avalanche observed on Banner Summit on Friday. This slide likely ran on a weak layer at the old snow surface.

  • Wind Slabs

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

    On Saturday, Chris observed more than a half-dozen natural slab avalanches in the northern Sawtooths, just south of this zone. Most of these had released on the aprons below cliff bands (photo above/right). The terrain in this zone is generally gentler than that found in the Sawtooths, but if you go out looking for steep and rocky terrain today you may encounter similar slabs.

    When low-density snow is blown into wind slabs and drifts, the difference in texture may be subtle. Today, drifted areas may still feel like powder, but may have just enough added cohesion that you could trigger a slab avalanche. In addition, as the sun warms the snow for the first time, the low-density powder will transform into denser, more cohesive snow. Slabs may be sitting atop weak old snow surfaces (facets and/or crusts) making them more reactive to your weight. Recognize that wind-loading also adds stress to the weak layers buried deeperin the snowpack (described in Problem 1 above). Any slab you trigger could step down to these deeper layers, producing a much larger, more dangerous avalanche. 

    (2/26/2021) Low-density new snow combined with wind created fresh drifts and wind slabs. These will be most common at upper elevations, but you may also find them on open, mid-elevation slopes—as indicated by the drift in the center of the photo.

Avalanche Discussion

TIME MARCHES ON

It may be hard to believe, but we are rocketing towards spring, whether we like it or not. If you live and play in the Wood River Valley you've had to deal with a bit of a bleak February. Baldy recorded 15.5" of snowfall over the month, just 40% of average. But hey, better than last February when only 3" fell! However, if you live in Stanley or Smiley Creek you've seen a long string of snowy days with only a few days without snowfall. Across the board, temperatures have been near or below seasonal averages.

As we step into the month of March, we are seeing a significant shift in this weather pattern. Dry conditions are forecast for this week, along with temperatures warming a bit more each day. If we can get solid overnight freezes, this combination of sunshine and warm temperatures will eventually help to increase the stability of the snowpack. However, this process takes time and isn't always pretty. The snowpack this year has behaved unpredictably and I expect that it will continue to do so through this transitional period. 

If you're out in the backcountry today, be aware that you are encountering a snowpack that is in the throes of change. Rapid changes in the snowpack are rarely pretty, and they often produce difficult to predict conditions. If we are lucky, this shift in the weather pattern will give our snowpack some time to heal the weak layers of snow buried within it. But don't expect that to happen in a day. Keep those layers of weak snow in mind as you travel and spend time thinking about the consequences of being caught in a slide in the terrain you are in.

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