Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Wet snow avalanche hazards will be a growing hazard as refrozen surface snow softens through the day. Have a route and time to return home that allows you to avoid being on or under steep slopes with mushy, wet snow. At mid and upper elevations, it remains possible to trigger dangerous avalanches that break three or more feet deep on old weak snow. Stick to low-angled terrain that's not below steep start zones. 

Lawinenprobleme

  • Loose Wet

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

    On steep slopes where you find more than a few inches of moist or wet snow near the surface, you can trigger wet loose avalanches that can drag you into gullies, rocks, and trees, or over cliffs. Keep a close eye on your partners, even on terrain that might seem relatively harmless in dry snow conditions. You can minimize your exposure to this hazard by sticking to slopes where the snow surface remains frozen, or slopes less than about 40 degrees, where sluffs of wet snow move slower and entrain less debris. The hazard will grow more widespread through the day as temperatures warm, and is likely most pronounced on shaded, mid-elevation slopes where the snow hasn't been worked by direct sun. 

    (3/6/2021) Debris from a very large natural avalanche that released at near the ridge and entrained wet snow - and dirt - on its descent. Slide noted 3/6; likely ran 3/5

  • Persistent Slabs

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

    Nevertheless, it persists. While finding a a steep slope with dry snow might seem like a lottery win, it's this terrain where you're most likely to trigger dangerous avalanches that break 3 to 6 feet deep on weak snow buried in late January. Stick to slopes less than about 30 degrees where the snow surface isn't frozen into a crust that supports you or your machine. Don't linger under steep start zones that are capped with cantilevered cornices. 

Avalanche Discussion

A week of sun and dramatic warming ended with Saturday's cold front and clouds. The trend culminated with 48 to 60 hours or so of above-freezing temperatures at 6000 feet and above. However, the warming manifested differently in valley bottoms and at low elevations; this terrain saw a distinct diurnal melt-freeze cycle, with morning lows in the 20s and afternoon highs in the 40s and 50s. Saturday's cold front and clouds reversed that pattern; at mid and upper elevations, temperatures have dropped 15 to 20 degrees, and this morning's lows are near 20 degrees. Valley bottom stations are showing temperatures near freezing. 

Wet snow avalanche hazards now exist primarily at low elevations. At mid-elevations today, windward slopes should stay refrozen, but isolated wet snow hazards may develop on shaded and leeward slopes as air temperatures warm back up above freezing.  The primary concern will be triggering wet loose avalanches on steep slopes. Most will be small, though the dense debris can be difficult to escape, so getting caught in one of these can have disproportionately serious consequences. The potential for large wet snow avalanches will be isolated to continuously steep slopes where slides run long distances and entrain large amounts of snow. Sinking more than six inches or so into wet snow is a good clue to these conditions. The easiest ways to mitigate this hazard is sticking to terrain where the snow surface remains frozen or is less than about 40 degrees. Where Saturday's snow squalls left an inch or more of new snow, melt-freeze crusts will be slower to break down. While this snow will get wet quickly, it's not enough to create a wet snow avalanche hazard on its own. 

Then there's our lurking Persistent Slab avalanche problem. On steep slopes where you find dry surface snow, consider the hazard little changed over the past week. Thicks slabs still sit above weak facets and surface hoar bured in late January. During the warming, slabs likely consolidated and the weak layers likely saw some sintering. But enough to eliminate that structure and the accompanying potential for people to trigger very dangerous avalanches? A flat no. So it's critical to maintain practices that minimize the chances and consequences of triggering a thick, dangerous slab. Slopes where the snow surface remains refrozen are less susceptible to human triggering. 

A few other isolated avalanche hazards exist today - Glide avalanches and cornice falls. Avoid being under wide cracks where bare ground is showing, and under ridges where you see thick cornices cantilevered over steep start zones. Falling cornices can produce enough debris to be dangerous, or they can trigger larger avalanches on steep slopes below them. 

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