Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The weight of recent snow is stressing the snowpack. You're could 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.

Problèmes avalancheux

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    This zone picked up 1-1.5" of SWE since Tuesday afternoon. This load was enough to cause a widespread avalanche cycle in the Sawtooths (observation). View Chris' ob here to see some of the recent avalanche activity from the Banner Summit area and the Northern Sawtooths. 

    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, recent observations indicate that at least some of these paths are capable of re-loading and running again. 

    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.

    (1/14/2021) Avalanche that released south of Copper Mountain. This slope avalanched during the Solstice storm and has become a "repeat offender". E, 8700'

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2

    Recent 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.

    Hard slabs can be tricky to deal with. You may be able to travel some distance out onto a slope before finding the "sweet spot" where the slope fractures leaving you little chance to escape. 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 Wednesday, strong to extreme W and NW wind continued to load slopes at all elevations. Skiers reported continued strong wind yesterday, rapidly filling in skin tracks at middle and upper elevations.  To give you an idea, you can look at these photos from Wednesday and yesterday and watch a short clip of the 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, tipped the scales across much of the forecast area. Continued wind-loading following the storm has only added to the problem. Yesterday, Chris observed avalanches near Copper Mountain. Some appear to have run in the same location as avalanches that failed during the previous cycle on January 4th and 5th. Widespread avalanche activity was observed along the Smoky Crest and north into the Sawtooths. While by no means a complete list, you can check out the ever-growing tally of observed avalanches on our interactive Avalanche Occurrence map here. 

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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