Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Pay attention to the snow surface while choosing your route today.  Recognize that pillowy dunes or scalloped texture is evidence of wind-drifted snow, and steer your path toward sheltered or scoured terrain for safer travel.  On sunny slopes, pinwheels and rollerballs indicate that the surface snow is moist and ready to slide. Take this as your cue to seek out shadier slopes or make an early exit.

Problemi valanghivi

  • Wind Slabs

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

    Observers noted moderate amounts of wind-transported snow throughout the day yesterday. Southwest winds have and will continue to increase in speed today. Plenty of recent low-density snow is available to keep the wind slab machine fueled.

    Expect to find recently formed and developing wind slabs 1 to 2 feet thick. These features will be found near ridgelines, on the sides of cross-loaded gullies, and near prominent terrain features. Slabs will thicken as you gain elevation.

    These features may present themselves as dune-shaped or scalloped surface. Cracks shooting out from your skis or sled are an obvious sign of instability. Wind-deposited snow will be stiffer and keep your skis or snowmobile closer to the surface.

     

    (2/2/2023)

    The most action we saw from recent wind-drifted snow.

  • Loose Wet

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

    The recent storm deposited 6-10 inches of low-density surface snow across the forecast area. Yesterday, warming temperatures and intermittent sunshine warmed the surface in areas sheltered from the wind and open to the sun. Today will be slightly warmer, and we expect the wet loose problem to be more widespread.

    This new snow rests on various surfaces, including crusts and windboard, which may allow slides to travel further than anticipated. If we see more sustained sunshine today than forecast, natural loose avalanche activity may occur on sunny aspects. Your first clues to this developing problem will be snow bombs falling from tree branches, meltwater dripping from trees, and snow peeling off rock faces. Rollerballs or pinwheels on steep slopes are signs directing you to a different aspect. Either stay ahead of the sun or stick to the shady side of the compass to limit your exposure to this problem.

    Loose Dry sluffs are still a concern on steep, shaded slopes. Cold temperatures and faceting slow the strengthening process in the loose surface snow. Expect to trigger and manage your sluffs today. Choose terrain with clean runouts to avoid tangling with surface obstacles. 

    (1/9/2023)

    Rollerballs triggered by turns on this mid-elevation, southeasterly slope. The rollerballs are 1-3 days old; the snow surface was not moist or wet at midday.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–3

    Buried facets and surface hoar appear to be slowly gaining strength, but recent snowfall and wind continue to test this layer.  This layer is 1-2 feet below the surface in the Flathead Range and Southern Glacier Park, and 1-3 feet below the surface in the Swan Range.  The best way to identify this hazard is to dig down and see if this weak layer is present. Where you do find it, choose lower-angle terrain free of overhead hazards and convexities.  Small avalanches have the potential to step down to buried weak layers.   Slopes with clean runouts are an excellent way to build a margin of safety into your day.

    (1/31/2023)

    Snowpit on SE aspect in the Swan Range.  Failed on a persistent weak layer 50cm from the surface,  ECT20.

    Photo: sw

Avalanche Discussion

Yesterday was a much needed dose of Vitamin D.  Warm sun, good visibility, generally tolerable winds made for a great day in the mountains.  Riders on shaded slopes enjoyed cold, dry powder that sluffed readily, while those on the sunny side found more variable conditions as the snow surface moistened and refroze. Regardless of whether they were on team shady or team sunny, most riders reported recently drifted snow and active wind transport. 

Today, we’ll increase the dosage of both sun and wind.  Southwest winds will continue to ramp up throughout the day and stiffen slabs on leeward terrain. I expect these slabs to be more sensitive and more widely distributed than the soft and isolated drifts observed over the last couple days.  Solar radiation will again moisten the snow surface on southerly aspects into mid elevation.  This process will be slowed some by yesterday’s sun crust and cooling from southwesterly winds.  Rollerballs and pinwheels are signs that the sun has overcome these obstacles and moistened the snow surface enough to cause loose wet avalanches.  

If your goal is to ski steep, shaded, and wind-sheltered slopes, remember it is still possible to trigger loose, dry avalanches like this one. These slides still pose a risk if they knock you off your line, through rocks and trees, over a cliff, or into a gully. 

We have removed the Persistent Slab problem from the Whitefish Range.  During the last two weeks, observations from this zone have not included natural or human-triggered avalanches, or propagating pit results associated with buried weak layers. 

Come one, come all! Flathead Avalanche Friends Fest, a four-day festival from Feb 8-11, has a full schedule with mini-clinics, a keynote speaker, après, and a Big-A$$ Raffle. A little something for everyone. We hope you can join us to celebrate our community, learn about snow, and support our safety mission. Learn more here.

Motorized Level 1 - Instructed by Eric Knoff and Six Points Avalanche Education from Tuesday, February 7, 2023, to Thursday, February 9, 2023. More details are here.

Regioni coperte