Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Natural and human-triggered avalanches are likely, especially as you climb in elevation. You'll encounter many types of avalanche threats as you move up or down or change aspects and as the day progresses. Safely traveling in or below avalanche paths today requires knowledge, experience, and focus.   

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    You could trigger soft wind slabs up to 3 feet thick in exposed terrain. Yesterday's heavy snowfall and wind formed slabs, drifts, and cornices near upper elevation ridgelines and possibly in some middle elevation terrain. Today's wind could continue building slabs and wind features in isolated areas. 

    Cornices, drifts, dunes, rippled snow surfaces, and chalky snow pillows are visible clues that the wind has been at work.  If you see cracks shooting out in front of your skis or boards, you've probably found a wind slab. If you feel the snow stiffen beneath your sled or skis, its time to steer clear of large or consequential avalanche paths.

    Cornices have grown substantially this week, and the most recent growth may be very soft; natural or human-triggered cornice fall can trigger wind slabs beneath cornices. Give large or overhanging cornices a wide berth.

    In wind-sheltered terrain, today's sunshine may consolidate and stiffen the fluffy powder near the surface. This process raises the possibility of natural or triggered avalanches involving yesterday's snowfall on very steep slopes. Conditions can change rapidly on sun-drenched avalanche paths.  

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–2

    You are very likely to trigger sluffs in steep terrain, and some of these could be big enough to knock you over or bury you. The chance of natural loose snow avalanches will rise as direct sunlight shines on steep slopes. The increased threat will follow the sun around the compass, beginning on E-SE aspects in the morning, moving to S-facing slopes by noon, and finishing on SW-W aspects in the afternoon. 

    Many of these slides will be small and relatively harmless; however, large slopes, chutes, and couloirs could produce big, powerful sluffs that could easily catch, injure, or bury people. Be aware of the terrain above you and where an avalanche could carry you. Don't underestimate the potential size of the sluffs. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    It would take some bad luck, but triggering a large, destructive 3-6 foot thick avalanche isn't off the table yet. These slides would fail on persistent weak layers (crusts, crusts and facets, or facets) in the middle or bottom of the snowpack. You're most likely to trigger them on middle and upper elevation slopes commonly exposed to the wind.  

    Persistent Slab avalanches can release in surprising ways. You can trigger them from flat or low-angle terrain long distances away from steep slopes, and they can break far above you. They can break hundreds or thousands of feet wide. Before triggering an avalanche, you probably won't experience snowpack collapsing or other obvious signs of instability. 

    You're most likely to trigger one of these beasts in steep, rocky, wind-swept alpine terrain and in the northeastern corner of this zone. Here, thin areas of the snowpack make it easier to trigger avalanches.

    (3/3/2024) The crown of this large avalanche near Valley Ck Lake north of Stanley is an estimated 3-5 feet tall. It probably involved persistent weak layers and failed on a NW-W aspect near 8900'. In the northern mountains, these large persistent avalanches are most likely where the snowpack is thinner: in the eastern side of the Banner Summit zone and the far northeastern corner of the Sawtooth & W Smoky zone (NE of HWY 21). 

    Photo: Sena Strenge

Avalanche Discussion

Weird weather produces weird avalanche conditions.

  • Yesterday's storm deposited 8-16" of unusually low density powder that we rarely experience. The intense March sun will rapidly change the avalanche equation in short time windows on some slopes.
  • The Friday-Monday storm deposited feet of snow while moderate to strong winds blew for days, another rarity. Yesterday's storm makes it difficult or impossible to see which slopes were heavily wind-loaded before Tuesday.
  • To top if off, we have persistent weak layers that have produced extensive avalanche activity earlier this season. Although they are now buried  "out of sight" (deep in the middle and bottom of the snowpack), they are not completely "out of mind." Large, destructive persistent slab avalanches are most likely in the eastern side of this zone where the snowpack is thinner. 

Be careful out there today. There isn't a single avalanche problem to focus our attention, and the combination of many avalanche problems, amazing skiing and riding conditions, and blue skies has "close call" or "avalanche accident" written all over it.  

Regioni coperte