Boletín de aludes

Bitterroot

West Central Montana Avalanche Center
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Peligro de aludes

Sat
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 6 months ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

New snow is overloading weak layers in the snowpack. Dig down and look for strong snow over weak snow. Where you find it, or suspect it exists, stay off slopes over 30 degrees and their immediate runouts. The largest and most dangerous avalanches will be found on northerly slopes.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    This week, we received our first reports of human-triggered persistent slab avalanches. In the Seeley Lake region, a snowmobiler triggered a large avalanche on northeast terrain (Click here for initial information.) Plus, we’ve had unstable test results throughout the Bitterroot Range. (Click here and here for observations.)

    While this avalanche problem exists on all aspects, avalanches will be the largest and easiest to trigger on northwest through east aspects. Human-triggered avalanches are likely in specific areas, where you find the right slab and weak layer combination.

    The snowpack has two distinct weak layers, one about a foot deep, and one about two feet deep. Both contain feathery surface hoar. We’ve found the shallower layer on all aspects at upper elevations, though it is weakest on northerly slopes. It will be easiest to trigger where the overlying snow is a harder slab, such as where old wind slabs exist from earlier this week. The deeper weak layer exists mostly on sheltered northerly aspects.

    Dig down and look for weak layers, as you may not see other signs of instability, such as cracking and collapsing. We recommend quick pits in multiple locations. Surface hoar will look like a thin grey line in the snowpack. In some places, the deeper weak layer may be sugary facets rather than surface hoar. If you find either of these weak layer types, or are at all unsure, stay off slopes over 30 degrees.

    (2/19/2026)

    Buried surface hoar under 10 inches of recent snow.

     

Avalanche Discussion

We’ve moved into a tricky period for snowpack management. We know weak layers exist, and we’ve seen human-triggered avalanches and easy propagations on extended column tests (Click here for our most recent observation). But, unlike nearby forecast centers, we haven’t received widespread reports of cracking, collapsing, or natural avalanches. This means the snowpack is unlikely to give you feedback before you trigger an avalanche. With conditions like this, discipline is required to make thorough observations and choose safe routes.

The best way to find weak layers is to dig down and look for them. Unfortunately, these weak layers are spatially variable in distribution and sensitivity. Often, surface hoar gets destroyed up high by wind and sun but survives to get buried in sheltered areas. A common trap is to dig at ridgetop and not find surface hoar, then trigger a surface hoar avalanche partway down your line.

Get your hands or shovel in the snow regularly. Even a quick hand pit can help you figure out where weak layers exist.

The largest avalanches are possible on northerly slopes, where the deeper of the two weak layers (the January drought layer) exists as surface hoar. Elsewhere, this layer is facets or a facet-crust combination.

The shallower surface hoar layer was formed last weekend and buried by this week’s snow. We’ve found it on some solar aspects, but the surface hoar is largest and most continuous on northerly aspects. So, like the January drought layer, triggering an avalanche on this layer is most likely on northerly slopes.

We are still collecting data on the sensitivity and distribution of the shallower buried surface hoar layer. Plus, we’ve seen new surface hoar growing on the snow surface, ready to get buried by our next snowfall. If you dig in the snow, please send us a picture of your pit wall, and let us know your elevation and aspect. If you see avalanches, cracking, or collapsing, please let us know. You can submit an observation here.

Storms throughout the west have created dangerous conditions. Our condolences go out to all involved in the tragic accident in California, plus the recent snowmobiler fatalities in Utah and British Columbia. Click here for a preliminary accident report from California, here for the one from Utah, and here for the one from British Columbia.

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