Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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

You could trigger an avalanche in wind-drifted snow above 6500'. Larger avalanches - though less likely - could fail on weak layers buried 1 to 2 feet deep. Choose slopes where the snow is not visibly affected by wind for safer, more enjoyable riding. Cold temperatures can complicate any emergency situation.

Problemi valanghivi

  • Wind Slabs

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

    Generally calm winds over the last 36 hours have limited the formation of fresh wind slabs. Older slabs of drifted snow have had some time to heal, though cold temperatures and underlying weak snow have slowed this process. Drifts may be found on all aspects at upper elevations due to changing wind directions. Isolated pockets of wind-affected snow may be found below 6500'.

    If you observe any blowing snow today, it will point in the direction of fresh slabs. Look for signs of wind-affected snow (like an etched surface, or dune-shaped featues) along ridges, saddles, and in open bowls. Cracking around your feet or machine is a sign of unstable snow, and a good reason to find a slope that is less steep or more sheltered from the wind. Hard slabs may support your weight, have a hollow sound, and can break well above you. Small surface slides could trigger a larger avalanche on a buried weak layer. 

    (2/10/2025)

    Steer away from slopes where the snow surface is visibly affected by the wind. Dune-shaped features indicate that this slope was cross loaded by recent NE winds. 

     Photo: Michael Reavis

Avalanche Discussion

Recent winds are the weakest we’ve seen since mid-January, but I have some reservations about dropping the wind slab problem:

  •  Abundant SAFT (snow available for transport) and a forecasted increase in southwesterly winds could result in fresh slabs by the end of the day.
  •  Recent cold temperatures have slowed the healing process for previously formed wind slabs.
  •  Wind slabs have formed on top of weak layers.
  • Limited observations from the alpine have increased my uncertainty. One observation from yesterday (Tuesday) suggests that winds were still moving snow at upper elevations over the last two days.

Despite cold temperatures, weather stations recorded decreases in snow height over the last two days. This is a hint that February’s snowfall is settling into a cohesive slab on top of the weak 1/31 interface. This is another box checked on our pre-flight list for Persistent Slab. We already listed this problem as "unlikely" in the Whitefish range, where observations have featured buried surface hoar, collapsing and, unstable pit test results. 

In the Flathead and Swan ranges, the potential for slabs to fail on buried weak layers is captured by the Wind Slab problem.  This is because wind-affected slopes have the stiffest surface snow and are better able to propagate a facture. As the snowpack continues to settle, the distribution of this hazard will grow to include sheltered slopes, and it is likely we will list Persistent Slab in these zones. On Tuesday, GNP staff visited a leeward (East) slope of Mount Brown where they found repeated unstable results on a layer of facets buried 1.5 feet deep. 

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