Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
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

Sustained easterly and northerly winds have transported snow onto typically windward aspects that face west and south. Cracking around your boards or machine and dune-shaped snow features are clues to change aspects in search of snow not affected by the wind. If you succeed in finding cohesionless snow and observe no signs of instability, ride one at a time while keeping your partner in sight. Choose concave or planar slopes with clean runouts. 

Problemi valanghivi

  • Wind Slabs

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

    Impressively strong wind speeds out of the east and north have finally begun to subside. Mount Aeneas in the Swan Range had sustained speeds averaging 40 mph for roughly 30 hours and Whitefish Mountain Resort reported winds above 15 mph for 48 hours. We did see a brief uptick in wind speeds at Hornet (Whitefish Range) and Tunnel Ridge (Flathead Range), which previously had not reached optimal speeds for building wind slabs. This data tells us that wind slabs may be distributed widely across the forecast area. Today, winds are forecast to be light, so you will have to rely on surface clues to identify where slabs of drifted snow exist. Wind textured surfaces that appear bulbous or pillowy are slabs of drifted snow. Steer around these on your hunt for powder snow.

    (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

Avalanche Discussion

On Tuesday, remote weather stations reported sustained wind speeds capable of transporting snow out of the east. Today, winds are forecast to drop in speed and switch directions back to the west this afternoon. Although we expect a shift in wind direction, it does not appear that winds will be strong enough to drift snow.

We received no new observations on Tuesday, leading us to a slightly higher than usual degree of uncertainty about the sensitivity of recently formed slabs. Two days ago, an avalanche professional in the Flathead Range triggered a small slab of drifted snow. He found wind drifted snow more widespread above roughly 5500 feet with slabs up to 3 feet thick. These thicker slabs were stubborn, meaning difficult to trigger. Other observations from the same day found cohesionless snow with minimal wind effect. I would expect more of the same today.

There are several generations of wind slabs that have formed over the past 3 days. Older slabs are thicker and will be more difficult for a person to trigger. However, if triggered, a hard slab failing 2 to 3 feet thick would be large enough to bury and injure a human. More recently formed slabs may still be reactive to the weight of a human. Wind drifted snow will vary from drainage to drainage due to localized and channeling winds. Slabs of drifted snow are on the trend towards stabilizing, yet I strongly suggest giving bigger terrain another day to adjust to the recent wind loading. Safer and better quality riding is in terrain sheltered from the wind.

You will notice we dropped Persistent Slab from the problem list. This decision is based on a lack of avalanche activity failing on buried weak layers. The last reported avalanche was on February 7th (observation). Pockets of buried surface hoar and near-surface facets still exist on northerly facing slopes, but appear to be dormant for now. 

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