Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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

Large hard slabs capable of snapping trees have failed in the past week. Avalanches can break above you and may give you no warning sign until it is too late. Choose lower angle slopes, or carefully select terrain that does not terminate in a stand of trees, gully, or cliff, where even a small slide can have a devastating outcome. 

Problemi valanghivi

  • Wind Slabs

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

    Yesterday (Sunday) observers noted blowing snow and recently formed drifts. Slabs of wind-drifted snow were stubborn to trigger and small in size. Expect slabs to become larger and more dangerous the higher you climb. Avoid dune-shaped pillows and areas where you observe active wind loading. Utilize small and inconsequential slopes to test the sensitivity of freshly formed drifts.

    (2/26/2023)

    A ski cut on the lee side of a cross-loaded, mid-elevation ridge released this small soft slab of drifted snow (SS-ASc-R1D1-I).

    Photo: br

  • Persistent Slabs

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

    Slabs resting on persistent weak layers exit above 5000 feet. Recent avalanche activity proves that slides can propagate wide distances and wrap around terrain features. Although triggering one of these deadly avalanches is becoming more difficult, the consequences can be fatal. Tracks on a slope do not indicate a slope is safe. 

    Managing terrain is critical. The most surefire way to avoid the problem is to stick to low-angle slopes that are not connected to steeper terrain. If you do decide to inch out into steeper terrain, choose slopes that are free of terrain traps and expose only one person at a time. Avoiding common trigger points on the slope, such as convex rollovers or where the slab is thinner can reduce your chances of triggering a large avalanche. 

Avalanche Discussion

Recent Avalanche Activity:

Flathead Range/southern Glacier National Park: Nearly everywhere. Observations have noted crowns 2+ feet thick above 5000 feet on aspects that primarily face north and east. Recent avalanche activity shows that slabs are breaking wider and thicker on upper-elevation slopes. This is likely a result of slab hardness due to more snowfall and wind loading. 

Swan Range: One recent noteworthy observation was of a large avalanche failing on a southwest-facing slope. This avalanche propagated a wide distance and was roughly 2 to 3 feet thick. Last week, Guy reported large and very large avalanches on almost every aspect south of our advisory areas in the Swan Range.

Whitefish Range: Observations of small slab avalanches occurred in the Apgars and Mt. Marston area in the past week. A noteworthy incident occurred in the Apgars 8 days ago where the 5th person down a slope triggered a slab avalanche (observation). This avalanche caught, carried, and partially buried the individual. This slab failed above a crust. Persistent weak layers are proving less common in the southern range, but are found above 6500 feet in the northern range. This part of the range is also the area that received more snowfall last week. 

Challenges of Managing Hard Slabs and Persistent Slabs

The biggest challenge of managing a hard slab, or a slab over a persistent weak layer is the lack of feedback we receive days after the loading event. Naturals are mostly over and obvious signs of instability, like collapsing and whumpfing become less common as the weak layer gets buried deeper. These kinds of avalanches are notorious for catching the 3rd or 4th person down the slope, thus making tracks on the slope untrustworthy. Slabs can break far above you and in unpredictable ways. Although triggering an avalanche is becoming more difficult with each passing day, the consequences are severe.

Regioni coperte