Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré last year. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Strong winds and fresh snow will increase the danger throughout the day. Triggering an avalanche in steep terrain is likely, especially where the wind has built drifts and stiffened the surface snow. Low-angle slopes sheltered from the wind will offer the safest and best quality snow. 

Problèmes avalancheux

  • Storm Slabs

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

    Another round of snowfall with elevated wind speeds began Saturday and will build fresh slabs throughout today. Fresh and wind-blown snow falls on various surfaces, including lower density snow, graupel, wind-board, and crusts.

    Slabs will become thicker and more widespread as you gain elevation. The largest and most dangerous features will be found in wind-drifted terrain, where it is likely that you could trigger a slide.  Avalanches in the new snow could step down into the foot or more recent snow, producing a much larger slide. 

    Today’s blowing snow and fresh cornice formation point toward areas with wind loading and elevated danger. Look for the tell-tale signs of a wind-affected surface, such as ripples or dunes. Cracking or collapsing indicates you have found an unstable slab, directing you to a lower-angle slope.

    (3/15/2025) 

    Riders could trigger soft slab avalanches in the recent snow, especially where the wind has formed drifts or stiffened the surface. This slab occurred in the Flathead Range on Saturday.

  • Persistent Slabs

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

    January's weak layers (facets, facets + crusts, surface hoar) lurk beneath a 2-4 foot slab. Their distribution is isolated, and triggering a large avalanche is unlikely but not impossible. Today's moderate to strong winds will load slopes harboring these layers, with this added stress potentially overloading the strength of these layers. 

    You could trigger one of these beasts where the weak layer is closer to the surface, such as in wind-affected terrain with variable slab depth. The edge of a slab generally thins and is an ideal location for triggering. Locations with rocks or small trees and brush sticking out of the slope are likely spots. Before initiating an avalanche, you may not experience noticeable signs of instability like snowpack cracking and collapsing.

    Today's surface slides or cornice fall could trigger a Persistent Slab avalanche.

    Digging into the snow is the only way to identify if your slope contains this layer. Choosing lower-angle terrain not connected to steep slopes is the easiest way to mitigate this problem.

     

    (3/10/2025)

    Recent avalanche activity in the Flathead Range/Marion Lake region. This rocky slope is an example of where a hard slab avalanche can be most likely triggered due to a variable slab depth. 

    Photo: Michael Reavis

Avalanche Discussion

Saturday's storm underproduced and tapered off around midnight. The Flathead Range and central Glacier Park were favored with around 9 inches of new snow and 0.7 inches of SWE. The Whitefish Range received similar amounts of SWE with about half as much snow. The typically soggy Noisy Basin in the Swan Range recorded lesser amounts. However, the backside or Hungry Horse reservoir side can deliver sneaky amounts of snow, but there are no weather stations to tell us what happened there. The nearby Emery Creek SNOTEL recorded 4 inches of fresh snow, and we expect the Doris and Lost Johnny areas to have picked up more than Noisy. 

Another precipitation pulse arrives this morning, with 3-6 inches of snow in all mountain locations by sunset. Storm snow from Saturday and today will develop soft slabs in sheltered locations. More importantly, the winds are forecast to ramp up throughout the day and become strong enough to transport snow at middle and upper elevations. This week's snowfall has left plenty of snow available for transport, and we expect active slab formation to occur in areas exposed to the wind.

Today's avalanche danger will increase throughout the day as storm snow accumulates and, more importantly, the wind transports snow. The avalanche danger in the Whitefish and Swan Range begins at MODERATE this morning but should rise to CONSIDERABLE by day's end. Dangerous avalanche conditions will develop, especially on wind-loaded slopes. The danger is elevated this morning in the Flathead Range, where more snow fell yesterday.

Saturday's observations were sparse, with just one public observation from the Flathead Range. This group intentionally triggered soft slab avalanches in the storm snow. I traveled east of the WMR ski resort to look at a few of the multiple rider-triggered slides from Thursday and Friday. Failure was noted in the density change between Thursday's drier snow and Friday's slightly wetter snow and beneath this recent snow on top of a stout crust.  

Curious about recent developments in tele boots and bindings? Check out Telefestivus at Blacktail Ski Area on Saturday, March 22, and Sunday, March 23. In conjunction with the mind-freeing event, Tamarack Brewing will host a fundraiser with a raffle and film for the Friends of the Flathead Avalanche Center from 5 to 8 PM Saturday, March 23. 

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