Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Expect to find fresh slabs of wind-drifted snow in unusual locations at all elevations. Utilize sluff management on steep slopes harboring loose, dry snow. Cold arctic air and bitter wind chills could turn a minor inconvenience into a severe problem. Keep your trip plan short and simple.

Problemi valanghivi

  • Loose Dry

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

    Sunday’s storm deposited 6-16” of low-density snow onto a melt-freeze crust, hard slab, or settled snow. On slopes steeper than about 35 degrees and sheltered from the wind, you may trigger long-running sluffs that could entrain substantial snow. Utilize sluff management techniques and limit time traveling above terrain traps.

    (2/16/2022)

    Localized small dry sluffs in steep terrain

    Photo: Mike Reavis

  • Wind Slabs

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

    Arctic air is responsible for moderate to strong north through east winds that are transporting Sunday’s low-density snow into slabs on atypical aspects. These unusual winds can often form slabs at low and mid-elevations. The recent snowfall may disguise older hard slabs overlying weak snow on northerly and easterly slopes. Look for etched snow, which may sound hollow. Cracking is a clue to seek out the ever-shrinking areas sheltered from the effects of the southwest and northeast winds.

    (2/20/2022)

    An accidently triggered soft slab in the Whitefish Range. This was triggered on a convex roll where the terrain went from less steep - to steep. The debris was not large enough to bury or injure a person. 

    Photo: Sara Boilen

  • Persistent Slabs

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

    Buried surface hoar and facets, 1-2 feet below the surface, may still be affected by the weight of a rider or their snowmachine in locations where a supportable surface crust does not exist. Continued propagation in snowpit tests confirms we are not out of the woods quite yet. If you choose to recreate in terrain on the north half of the compass, select planar slopes free of convexities to minimize your chances of triggering a slide. Choose areas with clean runouts free of surface obstacles that may limit the extent of trauma and burial if you are unlucky enough to awaken this layer.

Avalanche Discussion

Sunday's storm brought needed snowfall to most mountain locations and isolated valley floors. The distribution of the snowfall was spotty, but favored areas include 12" in West Glacier, 16" at Mt Brown, and 10-12" along Highway 2 from John F. Stevens Canyon to Marias Pass. The northern Whitefish Range picked up an inch of water with reports of around 16" at Mt Marston. The Noisy Basin SNOTEL in the Swan reported a half-inch of water.

A strong Arctic air mass nosed over the Continental Divide early Sunday morning and gradually made its way west reaching WMR by 2:00 PM. Moderate to strong east winds accompanied the cold air drifting Sunday's low-density snow onto west and south aspects. We can expect the cold temperatures and breezy winds to continue through Wednesday.

The avalanche danger remains elevated today in the areas favored by recent snowfall - the Whitefish Range, central Glacier Park, southern Glacier Park, and the Flathead Range. Fresh wind slabs on atypical aspects are our problem of concern. We have removed Storm Slab from today's problem list due to Sunday's snow lacking cohesive qualities. Due to this incohesive snow, we have added Loose Dry to today's avalanche problem list. 

Riders in the Whitefish Range accidentally triggered two slab avalanches on convexities in the Whitefish Range Sunday. Both had crowns between 6-10 inches, with the largest propagating 100 feet wide. Cam found older wind slabs propagating in snowpit tests on a north slope Sunday in the Flathead Range. These slabs were hard and resting on weak snow from earlier in the week. He and his partner were able to trigger small (D1-D1.5) Loose Dry slides which ran up to 500 vertical feet on top of a melt-freeze crust. Blase was in the Flathead Range, where his party observed the fresh snow sluffed easily on steep north slopes. Another group in the Flathead Range reported reactive hand pits, which led them to keep their slope angles less than 35 degrees. Riders in the Apgars observed cold, loose dry surface snow and good riding conditions with no signs of instability.

 

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