Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

The weight of recent snow is stressing the snowpack. You're likely to trigger large, destructive avalanches—especially in steep, recently wind-drifted terrain. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes.

Avalanche problems

  • Deep Persistent Slabs

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

    This zone picked up 1-1.5" of SWE since Tuesday afternoon. We don't have direct observations of the Banner Summit Zone since skies cleared yesterday but this load was enough to cause a widespread avalanche cycle in the Sawtooths and the Smoky Mountains. Avalanches occurred on many different aspects, in both obviously wind-loaded and generally sheltered terrain. Recent avalanche activity in neighboring zones is likely to have occurred on the weak layer of sugary facets that was buried in mid-December (video).

    There are some important differences in the Banner Summit Zone, primarily tied to the overall depth of this primary weak layer: 

    • Because the weak layer is so deep, it's getting more difficult to trigger avalanches involving this layer. 
    • On the flip side, avalanches you trigger on this layer may be very large—big enough to destroy vehicles and break large trees. 
    • Even though many slopes in this zone already avalanched during the Winter Solstice storm, a storm last week still produced some noteworthy slides (example, example).

    The added snowpack depth from this storm will make evaluating stability that much more difficult. Snowpack stability tests are less trustworthy, and snowpack collapses will be less frequent. In many cases, the first obvious sign of instability can be triggering a monster avalanche. Continue to choose low angled slopes and to pay extra attention to the terrain adjacent to them. Remotely triggering an avalanche from below, above, and to the sides of steep slopes remains a very real possibility.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Yesterday's strong to extreme SW-W-NW wind rapidly built fresh wind slabs. Expect to find both hard and soft slabs in many locations. These slabs will be thicker and more widespread at upper elevation, but touchy wind slabs may exist in exposed terrain at any elevation. Cracks shooting from your boards or sled are the best indication that you've found a sensitive slab. Wind slab avalanches that release near ridgelines could "step down", failing on layers deeper in the snowpack and becoming much wider than the initial avalanche. 

    Wednesday's strong to extreme wind built fresh wind slabs on many slopes.

Avalanche Discussion

Tuesday and Wednesday's storm dropped anywhere from 0.5-1.5" of SWE. For storm totals across the forecast area, check here. Although precipitation diminished early in the day yesterday, strong to extreme W and NW wind continued to load slopes at all elevations. As one observer stated, "we were looking up into the Boulders all day watching active wind transport and expecting naturals to release".  I shared the same thoughts as I walked out Titus Ridge near Galena Summit. You can see a short clip of active wind-loading here. 

The uncharacteristically weak nature of the facets in the lower third of the snowpack has produced widespread natural avalanche cycles with relatively light loads. This last storm, while not huge, again tipped the scales. Continued wind-loading for several hours following the storm has only added to the problem. Yesterday, as I looked south along the Smoky Crest nearly every steep slope between Titus Lake and Titus Peak had avalanched. Ben spotted numerous, meaty slab avalanches in the Sawtooths (photo, photo, photo). Large avalanches were also spotted in the Boulders. This of course is only a partial list. We didn't get a good look at the Soldiers, or mountains near Banner Summit but given the track record of this weak layer, it's not going out on a limb to expect to see evidence of natural activity there as well. 

The lure of fresh snow and mild weather over the next few days will be strong. Trust me, I get that, but I urge you to build an extra safety margin into your travel plans. The weak layer we're dealing with is special, but I hesitate to call it "unpredictable". We've seen what it can do, and we know it can be touchy for days after a loading event. Don't lose sight of those facts as you choose where to ride this weekend.  

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