Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
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Kernpunkte

Above 6500 feet, steer around lingering wind-loaded features, such as dunes, cornices, or cross-loaded slopes. Although unlikely, there is a slim chance that you can trigger a large avalanche on shaded aspects in steep, rocky terrain. If you notice wet surface snow and roller balls, start planning your exit or move to more shaded slopes with dry snow.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Southwest winds at upper elevations continue to drift this week's incremental snowfall. Fresh slabs will be generally thin and relatively small, found downwind of ridgelines, and in cross-loaded gullies. These may be easier to trigger, and break wider than expected, where snow drifted onto a recent melt-freeze crust. 

    Scalloped snow, scoured patches, and dunes indicate wind-affected surfaces. Look and feel for stiffer snow that may crack beneath your boards or machine. If you decide to ride steep terrain, choose slopes with clean runouts, minimizing the consequences of being swept downhill. There remains a chance that a wind slab avalanche could trigger a much larger hard slab avalanche, as described in the Persistent Slab problem below. 

    (3/24/2024)

    Freshly formed and fallen cornice from recent winds. These features along with scalloped snow, dunes, and scoured patches indicate wind-affected surfaces.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–3

    The chance of triggering a large avalanche on weak layers buried 2-4+ feet decreases as these layers gain strength. The most likely place to trigger one of these beasts is in steep, rocky, wind-swept terrain on the north side of the compass. Here, the weak layers are closer to the surface and possibly better preserved. 

    You may not notice signs of instability, such as collapsing or cracking before you trigger a slide. The resulting size of the avalanche would likely be unsurvivable. If you ride in steep terrain, opt for slopes with a thicker, more uniform snowpack and free from convexities. Steer around areas peppered with rocks where you are most likely to affect these weak layers. 

    (3/17/2024)

    This is a hard slab avalanche on Nyack Mountain that failed on a northeast aspect at upper elevations on March 16. This slide likely failed on a layer of facets above the early February crust.

    Photo: Mark Dundas

Avalanche Discussion

We settled into a springtime pattern of dynamic weather in the Flathead. Localized snowfall, light winds, and warming afternoon temperatures create an interesting mix of snow conditions. Although the snowpack has been trending in a more stable direction, changing surface conditions are likely, and require the attention of those who travel in the mountains.

Observers have confirmed a general trend of a supportable crust on southern aspects and up to 10 inches of soft snow on northerly aspects. An observation from Essex reported that their ski descent included significant roller balls and a sticky surface snow in the afternoon. This was similar to an observer in the southern Whitefish Range who described wet surface snow by the early afternoon on steep northerly slopes. Given that today’s weather is similar to yesterday, you can expect to encounter wet snow instabilities by the afternoon. Dry snow getting wet for the first time will be most unstable. Get ahead of these hazards by planning an early exit or by moving to shaded aspects that continue to hold dry snow.

We’ve dropped the Persistent Slab problem in the Swan Range. Repeated observations documented that this area’s buried weak layer is non-reactive, and with a lack of reported avalanches, we feel comfortable removing this problem. In the Flathead Range, Glacier National Park, and the Whitefish Range, the Persistent Slab problem remains unlikely but of high consequence. You can reduce your risk by avoiding rocky, steep, and heavily wind-affected terrain on shady slopes above 6500 feet.

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