Boletín de aludes

Bitterroot

West Central Montana Avalanche Center
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Peligro de aludes

Fri
Alta montaña
2 · Moderado
Límite del bosque
1 · Débil
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

It is possible to trigger a windslab avalanche today on multiple aspects due to shifting winds. Make careful assessments of wind features today and avoid wind loaded slopes over 35º. Loose dry avalanches are likely where the snow is not wind drifted. Take care around terrain traps where entrained sluff could push you into or over hazards. 

Problemas de aludes

  • Wind Slabs

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

    In the central Bitterroot, from about the West Fork of the Bitterroot River to Lolo Pass wind slab can be found on west and east aspects. 

    In the southern Bitterroot, winds blew from the south over the past couple of days and loaded north aspects. 

    Winds are currently westerly throughout the Bitterroot and loading east faces. Triggering a wind slab avalanche is possible today. 

    Keep in mind that multiple aspects hold reactive windslab. Tuesday and Wednesday, easterly and southerly winds loaded west and north slopes. Wind slab is forming on top of crusts from last week’s rain event and facets on previously scoured faces. Wind slab is found mainly at and below ridgeline, but exposed areas midslope may be cross-loaded—exercise caution in start zones and around the loaded edges of gullies. 

    Drifted snow, cornices, wide pillows, hollow-sounding snow, and shooting cracks all indicate the presence of windslab.  As windslab sets up and gets stiffer, or if it’s very specific in its location, you may not get shooting cracks as a warning sign. A good policy is to avoid any steep start zone expected to be wind loaded.

    Today avoid wind loaded slopes over 35º. Take special care to assess wind effects on multiple aspects. 

  • Loose Dry

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

    Up to 10” of new snow fell on Tuesday. Cold temperatures yesterday and last night have kept it soft and unconsolidated. Loose dry avalanches are likely on slopes over 38º. Due to the presence of the underlying crust from last week's rain, these were running far and fast yesterday.

    While mostly small, sluffs can create issues if encountered around terrain traps where they could push you off your feet and into or over train traps such as gullies or cliffs. Manage loose dry slides by letting them run before skiing, cutting out of sliding snow to high points, and riding ridges rather than gullies in steep terrain.

  • Persistent Slabs

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

    On north slopes above 8000’ in the southern Bitterroot, reactive buried facets could fail with the weight of a skier or rider. These are buried up to 3 feet deep. South winds have added to the loading. The potential exists for wind slab or cornice fall to step down to this layer. 

    Exercise extra caution in this zone. Avoid slopes over 35º in this zone.

Avalanche Discussion

Since the last forecast, up to 10” of snow has fallen in the Bitterroot. The southern portion received the bulk of the snowfall. Temperatures dipped to -4  overnight. Winds have switched from west to east and south and back to the west, loading multiple aspects.

Today, expect temperatures to the mid-20s. Winds are out of the west and moderate to strong. Partial cloud cover may limit solar warming. 

Sub-zero overnight temperatures and cold days have kept the new snow soft and promoted faceting. This has kept cohesive storm slab from forming. As temperatures warm over the next couple of days, we could see more cohesion in the snow and potential slabs on the rain crust. Slab formation will be accelerated on south aspects if the sun appears. The southern Bitterroot, with deeper snow, is at higher risk of storm slab forming with consolidation. 

The crust from last week's rain is still prominent and impacts skiing in most places. It’s currently proving to be a slick bed surface for loose dry avalanches. When the next round of snow, arriving Sunday, buries it deeper with a cohesive slab, we could see a widespread avalanche cycle.

Please let us know what you are finding out there. You can submit observations here.

Ski and ride safe.

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