Boletín de aludes

Flathead Range & Glacier NP

Flathead Avalanche Center
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Peligro de aludes

Tue
Alta montaña
4 · Fuerte
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Dangerous avalanche conditions remain following Sunday's storm. You can likely trigger a slide in new and drifted snow. Rain-saturated snow will be easy to trigger. Slides that start in near-surface snow could initiate a much larger avalanche on buried weak layers. Continue to give steep slopes and connected terrain a wide berth.

Problemas de aludes

  • Storm Slabs

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

    10-20 inches of recent dense snow rests on softer, drier snow, where the temperatures remained cold enough to produce all snow. The inverted near-surface conditions have decreased stability in the new snow. The most dangerous slopes are where the storm's moderate to strong winds built thick and stiff slabs of wind-blown snow. 

    The natural avalanche cycle is likely over; however, triggering a slide large enough to bury someone remains very likely. 

    Avalanches in the new snow have the potential to initiate a larger, more dangerous slide on buried weak layers. Avoid steep slopes, overhead hazards, and the runouts of avalanche paths.

     

    (4/7/2024)

    This avalanche failed in the storm snow and is a soft slab avalanche. This is the type of slide that could occur with a storm slab problem.

    Photo: Jeff Metsky

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2.5

    Recent snow, rain, and wind have added weight and cohesion to surface snow resting on weak layers buried 1-4 feet deep. Saturday, some slopes reached their breaking point, resulting in natural avalanches failing on sugary facets, surface hoar, or faceted crusts. Today, other slopes may be teetering on the edge, waiting for a human trigger.

    Conditions are most dangerous where wind-blown snow forms thick, stiff slabs; however, avalanches are also likely to occur in sheltered terrain. 

    Persistent Slabs can be triggered from flatter terrain at the top, bottom, or sides of steep slopes. Avoid avalanche terrain, including connected lower-angle slopes.

     

    (2/23/2025)

    The blue arrow points to the crown of a large avalanche on Nyack Mountain. During recent heavy snow and wind-loading, this hard slab avalanche probably failed on buried weak layers. This slide illustrates our Persistent Slab problem.

    Photo: Mark Dundas

  • Loose Wet

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

    Heavy rain saturated the snow surface below roughly 5500-6000 feet, where a natural wet avalanche cycle likely occurred. Continued warm temperatures allow these slopes to remain wet and weak, and triggering a loose slide is likely on steep terrain. Wet slabs remain a concern in this zone as recent rain percolates into the snowpack. 

    Above the rain line, fresh snow may sluff naturally or be triggered by a rider. Rollerballs and snow falling from trees or rock faces are often the first signs of warming snow.

    Move to a lower-angle slope free of overhead hazards if you note signs of instability, such as sinking into a mushy snow surface.

    Surface slides could trigger a larger slide on buried weak layers described in our Persistent Slab problem.

    (3/17/2024)

    This is a view of about a dozen wet loose slides originating on south-facing mid-elevation slopes. Heavy rain and rising freezing levels likely produced slides like these during the Atmospheric River event.

    Photo: Mark Dundas

Avalanche Discussion

The Atmospheric River arrived late Saturday evening and is wrapping up its impact on the Flathead this morning (Monday). Precipitation came in two waves separated by a generally dry mid-day Sunday. Precipitation totals (SWE or water) include 1.5 inches in the Swan Range, 2 inches in the Whitefish Range, and over 2 inches in Glacier Park. Warm temperatures accompanied this moisture, with the rain/snow line fluctuating between 5000-6000 feet.  Moderate winds with strong to extreme gusts transported snow at upper elevations.

Conditions remain dangerous, and we advise you not to travel in avalanche terrain today. There will be fresh snow to enjoy on low-angle slopes on Tuesday, warm temperatures with mostly clear skies, and good visibility for the remainder of the week. Plan on returning to the mountains on those days for a safer and more enjoyable experience.

Observations of avalanche terrain were limited by Sunday's cloud cover. I noted a large avalanche on the east face of Nyack Mountain that probably failed on buried weak layers. This face had several other surface slabs, but the lighting was poor. The BNSF avalanche team noted widespread wet loose avalanche activity, with sizes ranging from destructive sizes 1 to 2 (D1-2). They also observed several crowns but battled poor visibility.

Improving visibility this week will allow the FAC team to document avalanche activity associated with the Atmospheric River. We are most interested in how the buried weak layers responded to a significant warm loading event. Please submit any photos you take of the recent avalanche activity. Thanks!

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  • Feb 26th - State of our Snowpack Presentation at 7 pm for Pint Night at Blackstar with donations going to Flathead Avalanche! 

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