Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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

In sintesi

A simple plan is best today. Wind is forming unstable drifts in unusual locations and straining buried weak layers. Large natural avalanches occurred within the last two days. Extremely cold temperatures will complicate any mishap.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Rapid wind loading is straining  weak layers buried in the snowpack. Recent loading increases the possibility that you might trigger a deadly avalanche. Small sluffs or wind slabs can step down to a deeply buried weak layer and cause a more destructive avalanches.  The only way to manage this problem today is through effective terrain management - avoid traveling on and below steep slopes.

    (2/21/2023)

    A large avalanche at mid-elevations in Crystal Creek. We noted a handful of similar size slides in this area.

    Photo: Cam

  • Wind Slabs

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

    Strong northeasterly winds continue to build drifts several feet thick in unusual locations. Expect larger and more reactive drifts on slopes where you see blowing snow today.  Still be alert for drifts on typical leeward terrain (NW through NE to SE), as a few weather stations are still reporting Southerly winds.  You might find isolated slabs at low elevations, where winds have been fierce but drifting has generally been limited by amount of snow available. Slabs of drifted snow form below corniced ridgelines, in cross-loaded gullies, or down-wind of rollovers. Watch for shooting cracks or collapses that warn you of unstable snow and take this as a cue to seek out wind-sheltered terrain. 

    Loose Dry: The surface snow remains loose in many areas sheltered from the wind. Anticipate triggering a Loose Dry (sluff) on slopes steeper than 35 degrees.  Manage your sluff and limit time spent above terrain traps or in long-running gullies.

    (2/22/2023)

    Moderate to strong north and east winds transported substantial snow along the Swan front.

    Photo: Chris Gotschalk

Avalanche Discussion

The National Weather Service in Missoula spelled things out pretty clearly today:

"... frostbite could occur in as little as 5 minutes west of the divide this morning due to dangerously cold wind chills….”

That alone should steer you to simplify your plan if you’re heading into the backcountry today. Also featured on “Rob’s Reasons to Keep it Simple”:

  • Limited observations during the current arctic intrusion mean more uncertainty regarding the snowpack.
  • The two (valley-based) observations we received yesterday featured red flags, including:

Extreme weather, uncertainty from limited information, and red flags are good reasons to fall back on conservative terrain choices.  When combined, it’s time to seriously scrutinize your trip plan, double-check your gear, and build in margins for safety.

Regioni coperte