Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

It remains possible to trigger a slab avalanche on shaded aspects (NW, N, NE, E, SE), mainly where winds drifted snow into thicker slabs at upper elevations. Reduce the chances of triggering an avalanche by choosing slopes sheltered from the wind or slopes facing south. Hedge your bets by selecting slopes with clean runouts and only expose one rider to steep slopes at a time.

Problemi valanghivi

  • Persistent Slabs

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

    You are most likely to find trouble on shaded aspects at upper-elevations. These are the aspects and elevations where this weekend’s storm deposited enough snow to form a slab ontop of buried weak layers of surface hoar and facets. Shaded aspects along ridge crests are also where winds drifted snow into thicker stabs. We suspect the avalanche problem to be small and isolated at mid-elevations. 

    Reduce your chances of encountering this problem by choosing slopes that face south. If you want to ride on north and east facing slopes, pay close attention to signs of instability. Shooting cracks and whumpfing collapses are two signs you’ve found the problem. If in doubt, choose lower-angled slopes.

    (12/9/2024) Crown profile on a northeast aspect at 6500 feet. This avalanche failed on buried surface hoar. Photo: Cameron Johnson

Avalanche Discussion

We transitioned to a persistent slab avalanche problem throughout the forecast area. Unfortunately, there isn’t a clear picture to where this problem exists yet. We are most concerned about areas where winds drifted snow into cohesive slabs and areas favored by recent snowfall (N. Whitefish Range and Central Glacier National Park). Snow totals varied from a couple inches to a foot and half. This recent snow is resting on a fragile layer of surface hoar (a persistent weak layer). The variability of recent storm totals, plus the spotty, tricky nature of surface hoar, will make your field assessments critical. Here are some useful questions to ask while traveling:

  1. How much recent snow is there? You can do this with quick handpits. Dig down until you hit a crust, see a grey stripe (surface hoar), or feel for sugary snow. If you only find a few inches of recent snow, then there is not enough snow to form a slab. If you find 8+ inches of snow sitting on surface hoar, then you've likely found the problem.
  2. What aspect am I on? Slopes where this problem exists are on slopes shaded from the sun. The sun destroyed the surface hoar on solar aspects before it was buried. Observations generally describe a stable snowpack on south facing slopes.
  3. Where did wind transport snow? Continuously assess surface conditions and signs of wind drifting. Remain leery of dune-shaped drifts and pillowy-looking surfaces downwind of ridgelines and saddles. Slabs of drifted snow rest on persistent weak layers in many areas. This makes them more susceptible to triggering long after a loading event.

A storm enters the region this weekend. Models show anywhere from 5 to 15 inches of new snow with moderate to strong winds. Expect to see changing avalanche conditions soon.

Did you hear about the app? You can now access our region's forecasts, observations, and weather data directly from the Avy App (IOS; Android). Many features are accessible offline, so you can win debates about the avalanche problems right in the backcountry or submit an obs while driving home. 

Are you looking for avalanche education opportunities? Check out our calendar for upcoming events. 

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