Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Tue
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

An avalanche warning has been issued. Very dangerous avalanches conditions exist. Human triggered avalanches breaking up to three feet thick are likely. If caught, these avalanches will be difficult to survive. Seek out slopes with angles less than 30 degrees in steepness and avoid convex rolls where triggering an avalanche is more likely. The higher you go in elevation, the greater the avalanche risk is.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    The avalanche hazard remains elevated due to a weak layer of surface hoar buried up to 3 feet deep. Recent avalanche activity is our sign to stay off of and out from underneath avalanche-prone terrain. Feedback may become more sparse the further we get from the previous loading event. You may not receive feedback that a slope is unstable until it is too late. Fun and safe riding can be found on low angled slopes and open meadows that are not threatened by avalanche hazards above.

    (2/6/2021) A snowmobiler caught and carried on Saturday, February 6th. No injuries were sustained.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Recent snow and varying winds have stiffened snow into a cohesive slab on all aspects. Slabs may break up to a foot thick and even thicker near ridgelines where winds drifted recent snow. Since Saturday, winds have blown from almost all directions. Look for signs of drifted snow in unusual locations, like south and west aspects. The thickest and most dangerous slabs will be an older generation of wind drifted snow that formed during the storm on NW, NE, to SE aspects.

    (2/4/2021) Surface hoar buried 1-2 feet deep

Avalanche Discussion

Since January 30th, 15 people have lost their lives in avalanches in the U.S. This is the most avalanche fatalities in a seven day period since 1920 (when the Wellington avalanche disaster in Washington occurred and killed 96 people).  Five of these events involved multiple burials and deaths (NYT article). These accidents are a reminder for all of us to take a step back and be extra cautious.

We are sad to report that one of these fatalities was in our back yard. On Saturday, a group of snowmobilers was caught, carried, and one killed. The most up to date information on this accident are found here. We will update you as more information becomes available. Our condolences go out to all of the friends and family of the victims of these tragic accidents. We thank the rescuers who accept large amounts of risk during these events.

Recent avalanches and there is no shortage of them, are our sign to dial back our terrain choices. Patience is critical when dealing with a persistent weak layer, like the one we have. This layer of surface hoar is unique because it sits either on a firm layer of wind packed snow or directly on top of a slick rain crust. If the layer of surface hoar is not there, a layer of near surface facets rests in a similar location. This kind of setup persists for a long time and results in slides propagating far distances, pulling back into slopes that are 30 to 35 degrees in steepness, and running at fast rates of speed. There is a lack of evidence that this specific problem exists on the south and southwest aspects; therefore, we have reduced persistent slabs distribution. Most of the recent avalanches have occurred on north, northeast, and east aspects and above roughly 5800’. As you gain elevation, progressively dial back your terrain choices and avoid avalanche terrain altogether at upper elevations.

Many remote weather stations are showing roughly 2 inches of settlement in the last 24 hours. This tells us that recent storm snow is settling into a slab. I would suspect that the thickest and most dangerous slabs on NW to NE to SE aspects where strong winds transported storm snow last week. This is also where the hot spot of persistent slab avalanches have occurred. Since Saturday, winds shifted to the north, and today, we will see a more easterly wind. Wind speeds are mostly averaging in the single digits or around 10 to 12 mph. I would expect to find small wind slabs in non-typical locations near ridgelines.

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