Lawinenlagebericht

Swan Range

Flathead Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 9 months ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

With close to 2 feet of new snow, warming temps, increasing and gusty winds, and more snow coming today, avalanches large enough to bury a person are likely. This problem exists in all aspects at middle and upper elevations, not just in wind-loaded terrain. You can test the new snow, but the surest bet is to steer clear of steep slopes where storm totals exceed 8 inches.

Lawinenprobleme

  • Storm Slabs

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

    Favored locations in the Swan Range, like Noisy Basin, have picked up close to 2 feet of snow in the last 48 hours. With all this new snow, warming temperatures, and pulses of heavier precipitation, we can’t pinpoint where any weak layers might be. Avalanches could break anywhere within the new snow, at the various storm interfaces, or even deeper on a buried ice crust 1.5 to 3 feet below the surface. In wind-exposed terrain, slabs will be deeper, harder, and more capable of wide propagation.

    You’ve got two options for safe travel today. You can avoid steep slopes altogether, or you can make careful, ongoing assessments as you go. If you choose the latter, keep your tour conservative and have backup terrain to keep you off steep slopes if you encounter unstable snow. Recent avalanches are your biggest red flag, but if you can’t see out there, this may not be much help. Probe for how much new snow you’re standing on; where totals are higher, both the likelihood and the size of avalanches go up. Stomp on small, safe test features to see how the snow reacts, and watch for cracking, collapsing, or hard-over-soft snow. Start small and step back at the first sign of instability. If precipitation rates start pushing an inch an hour and/or you see blowing snow, treat that as a clear warning that avalanche potential is rising fast.

    (2/24/2023)

    This image is a soft slab avalanche in a sheltered location on a convexity. This slide occurred in a previous season, but it is the type of avalanche you may encounter today at middle and upper elevations.

    Photo: md

Avalanche Discussion

While the storm hasn’t delivered evenly across the map, favored terrain has been hammered. At Noisy Basin, we’re already hitting the thresholds that raise our hackles: 1 inch of SWE in the last 24 hours, 2 inches in 48 hours, and 0.4 inches in the last 2 hours. The snowpack has settled significantly, adding only 8” of total snow depth at 6000 feet, despite what fell from the sky. Sustained winds are only approaching transport speeds, but gusts in the 30s are more than capable of moving this new snow.

This sets up an if/then day. If you find a lot of recent snow, danger is higher. If you see blowing snow, danger is higher. If precipitation rates ramp up again, you get the picture. Parts of the Swan that received much less snow may have a less pronounced danger. Regardless, with snow levels creeping up to 4000 feet, new snow will fall heavier and denser than what fell earlier, creating the potential for an upside-down, slabby structure.

Yesterday, Guy and Mike found good riding and only minimal slab development, with an open question about a crust buried beneath all the recent snow. Elsewhere in the range, observers already reported cracking in new slabs and signs of wind transport even before last night’s uptick in weather. With all of this new load, tread lightly, and be especially wary on wind-exposed slopes in the lee.

Finally, models again show a bump in precipitation and winds this afternoon, so even if conditions feel manageable during the day, be ready for danger to rise later on.

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