Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
Open full map
Non aggiornato — questo bollettino è scaduto 5 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The threat of avalanches is greatest in upper elevation terrain where the wind has been at work. Smaller slabs formed at the surface will be the most reactive, while slides failing at the base of the storm snow will be larger and big enough to bury you. Small dry and wet loose avalanches will fail naturally as the sun melts the snow surface. Some may become large in very steep, rocky terrain. Underneath the new snow, buried persistent weak layers are grumbling from the weight. Any avalanche that breaks down on these layers will be tree-snapping and unsurvivable. Smaller slides failing in the new snow can break down to these layers.

The elevated hazard at low elevations is for the terrain around Lolo Pass. Much of the low elevation terrain in this zone was bare and snow-free prior to this week's storm.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    This week's storms brought 4-6 feet of accumulating snow to the mountains. The crest of the Bitterroot were the big winners, but peaks further east towards the range front and Lolo and Lost Trail Passes all tallied impressive totals. You'll be most likely to find instabilities within the new snow on slopes where the wind has been at work. Thinner wind slabs from recent winds will be the most reactive, but are likely to be on the smaller side. Slabs that fail at the base of the new snow will be much larger, easily big enough to bury you. 

    Look for signs that the wind has been work to help you identify recent wind slabs. Textured snow surfaces, smooth pillows below ridgelines and on the sides of gullies, and fresh cornices are all good indicators of wind transport and deposition. Cracking in fresh drifts is a sign you've found a reactive slab, but don't expect to get much direct feedback on instabilities at the base of the new snow. Reactive slabs will be most widespread in upper elevation terrain, but you may find similar slabs in exposed middle elevation terrain as well.

    Slides triggered in the recent snow can step down to deeper weak layers, producing very large, unsurvivable avalanches. More on this in the Persistent Slab problem section below.

    (3/13/2026) Photo: West Central Montana Avalanche Center

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3.5

    Weak layers buried in January and February are now 4-7 feet below the snow surface. Avalanches were failing on these layers right up until the start of this week's storm (see photo at right/above). Observations have been limited in recent days (it's been hard to see much with the constant snowfall), but we expect that very large slides have continued to fail on these weak layers during the storm.

    Any avalanche that breaks down into these weak layers will break widely and put massive amounts of snow into motion. Slides may run long distances into flat terrain and timber at the base of steeper slopes, and would be unsurvivable. The most likely trigger for these beasts are avalanches that fail in the new snow, large cornices collapsing and impacting the slope below, and deep track penetration on your snowmobile. Limit your time in the runouts of large avalanche paths. Completely avoiding this problem includes avoiding avalanche terrain threatened from above.

    (3/7/2026)

    Tracks and crown of a large skier-triggered avalanche in the backcountry terrain adjacent to Lost Trail that was triggered on March 6th. The avalanche failed around two feet down on a layer of surface hoar that was buried in mid-February.

    Photo: Ben VandenBos

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    Bright March sunshine on fresh snow will produce rounds of dry and wet loose avalanches today. These will be most likely on steep, rocky slopes facing the sun, and will generally be small. Many of these will release naturally through the day, following the sun as it arcs across the sky. Cool temperatures and variable cloud cover may help limit this problem, but if its warm and sunny and the snow surface is becoming wet where you are playing, these slides should be on your mind. 

Avalanche Discussion

While avalanche danger is decreasing, the likelihood of having an accident in our mountains is not. Today is the first sunny day after an impressive series of storms. Its been a tough winter, and we are all hungry for powder, but today is a good day to temper your goals and expectations. 

We are coming up for air on the tail end of the largest storm of the year. For the past four days, it was wet, wild, and windy out there, with fluctuating rain lines, strong to extreme winds, and days of heavy snowfall. Go out into the mountains today expecting to see a completely transformed landscape. The most likely avalanches today will involve the recent snow. Small wind slabs at the surface may be easy to trigger, but larger slabs breaking at the base of the new snow will be a real possibility and easily large enough to bury you. Rounds of small dry and wet loose sluffs will be occurring through the day, but cooler temperatures and variable cloud cover should help limit the size of these slides. However, if its warmer and clearer than forecast, some wet snow avalanches that start in steep, rocky terrain may become large. Many slopes have stout crusts underneath the new snow and avalanches that fail above them may run fast and far.

 Underneath the deep stack of new snow, you'll find weak layers that are grumbling under the load. These layers were producing dangerous avalanches prior to this week's storm, and they will need some time to adjust to the added weight. Smaller avalanches failing within the new snow (wind slabs and loose snow sluffs) can be effective triggers for these weak layers. Very large cornices that formed during the storm may be peeling off ridgelines as the day warms up, serving as "great" triggers for larger avalanches. 

 Today is a great day to get out in the mountains and enjoy a taste of winter, but we encourage you to do so cautiously. There is a lot of amazing riding and skiing to be done on low angle terrain free of avalanche hazard today. The storm snow is settling and there is some cold, dry snow on top from yesterday's cold front; a perfect recipe for low angle wiggling. The meadows are refreshed and deep, and the soft snow at the surface won't survive for long. Enjoy the beautiful day, but don't let it distract you from the dangers our snowpack presents. And remember, its never a good day if you don't come home with all of your partners.

Let us know what you are seeing out there. We'd love to see some photos of your tracks and powder-covered faces in the sun. You can submit an observation here; we really appreciate your time. 

Regioni coperte