Bollettino valanghe

Whitefish Range

Flathead Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Recent east and north winds drifted snow into slabs on the leeward side of ridges and gullies. South and west winds will increase throughout the day, drifting snow into reactive thin slabs. Shooting cracks and dune-shaped drifts are signs you’ve found a wind slab. Seek out terrain sheltered from the wind for the safest and best riding conditions.

Problemi valanghivi

  • Wind Slabs

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

    Observers yesterday (Sunday) triggered small slabs of wind-drifted snow. Slabs were found on almost every aspect above 5000 feet. Today, tuck in below ridgelines where recent north and east winds drifted snow into firm slabs. Pay attention to active wind transport today due to winds shifting back to a westerly flow, building fresh slabs on west and north aspects. Shooting cracks around your board or machine, pillowy-looking drifts, and hollow-feeling slabs are all signs you’ve found a wind slab. Terrain-sheltered from the wind is your safest option for managing this problem.

    (1/29/2023)

    Triggered shooting cracks in wind-drifted snow. 

    Photo: Cam

  • Persistent Slabs

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

    Weak layers of facets and surface hoar can be found 1 to 2 feet below the surface. So far, these layers are proving less of a concern and more difficult to find than in the neighboring Swan Range. Riders have experienced audible collapses in the Flathead Range recently. West and southerly-facing slopes are less likely to harbor a weak layer of surface hoar.

    (1/29/2023)

    Surface hoar is now buried 2 to 3 feet (70 to 90 cm) below the surface in terrain sheltered from the wind. This layer is highlighted by the black card in the snow. 

    Photo: Cam

Avalanche Discussion

Arctic air will begin to subside due to shifting wind directions. Upper elevation wind stations shifted from east to south overnight. The trend will continue to a westerly flow today while speeds slowly increase into the afternoon.

Shifting wind directions drifted snow onto various aspects in the past four days, making it challenging to find snow protected from the wind. Observations from all three ranges did find quality riding on southerly aspects. The key is to tuck in below where winds formed slabs near ridgelines. Riders intentionally and unintentionally triggered small soft slabs and sluffs in steep terrain. All reported avalanches yesterday were small in size, but worth noting if you have ideas of bigger terrain. Continue to give slopes with signs of wind-drifted snow a wide margin since cold temperatures slow the healing process, making slabs susceptible to human triggering. 

Persistent weak layers, specifically in the Swan Range, are buried at depths where they are hard to trigger. Yesterday, we found this weak layer 2 to 3 feet below the surface on a north aspect. At this depth, feedback and human triggers will become less common, but more dangerous. Tracks on a slope are not a tool for assessing this problem. Hitting a thin spot, convexity, or punching through with your track may cause this layer to collapse, triggering a large and deadly avalanche. Keeping slope angles low where this layer exists (primarily north and east aspects) is the easiest way to manage this problem.

Regioni coperte