Lawinenlagebericht

Seeley Lake

West Central Montana Avalanche Center
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Lawinengefahr

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

Kernpunkte

Skiers and riders are likely to trigger fresh wind slabs on upper elevation slopes today. Stay alert for signs of instability, like shooting cracks, collapsing, and recent avalanches. The best way to manage the hazard is to avoid steep, wind loaded slopes with smooth-looking pillows of drifted snow. Although unlikely, a smaller wind slab avalanche could also step down and trigger a larger persistent slab avalanche. 

Wind slabs will continue to grow tonight as another small storm impacts the region.

Lawinenprobleme

  • Wind Slabs

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

    Moderate to strong shifting winds drifted 6 inches of recent snow into fresh wind slabs at upper elevations. North and east aspects have the deepest drifts. Skiers and riders are likely to trigger these wind slabs near ridge tops and along the edges of gullies. The wind slabs are up to 12-24” deep and could be large enough to bury you. They may be especially sensitive because they lie on weak, faceted snow and surface hoar in many locations. A smaller wind slab avalanche could also step down to weak layers buried near the ground and trigger a larger persistent slab avalanche. 

    Stay alert for shooting cracks and smooth pillows of drifted snow. Cornices, wind lips, and drifts all indicate wind direction and loading. The best way to manage the hazard is to avoid steep, wind loaded slopes. Wind slabs will continue to grow tonight as another small storm impacts the region.

  • Persistent Slabs

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

    Triggering a persistent slab avalanche on upper elevation north and east aspects is unlikely, but not impossible. A poor snowpack structure exists where weak depth hoar is buried 1 to 3 feet deep under a slab. The slab is slowly growing as new snow accumulates on top. As the slab grows, the problem may become more sensitive. 

    Over the last several weeks, obvious signs of persistent slab instability became hard to find. However, that does not mean the deeper weak layers are trustworthy. Yesterday, we found propagating snowpit tests failing on weak depth hoar buried near the ground in the Seeley Lake zone. 

    Dig into the snow, and look for weak or sugary snow beneath a denser slab. If you find this poor structure, consider sticking to slopes less than 30 degrees in steepness. Also, remember that a smaller wind slab avalanche could step down and trigger one of these larger persistent slabs. Watch out for signs of instability like cracking, collapsing, and recent avalanches.

Avalanche Discussion

Although yesterday’s storm was generally underwhelming, we managed to enter a more active weather pattern - and with active weather comes increasing avalanche danger. 

Yesterday, we found 6” of new snow drifting into 12-24” thick fresh wind slabs in the Seeley Lake zone. The Bitterroot and Rattlesnake zones received less snow, so wind slabs in those zones will be smaller. 

Tonight, light snow will continue and accumulate up to 3 to 6 inches through tomorrow. A stronger storm is forecast to arrive Monday night, with moderate to heavy snow continuing into Wednesday. 

Before the recent snowfall, snow surfaces throughout the forecast region were weak, with widespread facets and surface hoar. South aspects were sun crusted. Strong winds may have destroyed these weak surfaces in some areas, but they likely remain in others. The weak old snow surfaces will make fresh avalanche problems especially sensitive. As fresh snow accumulates and builds a slab, it may begin acting more like a persistent slab problem than a wind slab problem. This means that it could remain sensitive for longer, and that you could trigger avalanches remotely, from adjacent slopes. Additionally, fresh snow will add load to the snowpack and may reactivate older weak layers buried near the ground. 

If the forecast (and our wishes) come true, and significant snow falls, we can expect the avalanche danger to rise. Stay alert for changing conditions. 

Remember that our snowpack is still thin. Hazards such as buried stumps, logs, and rocks are widespread and may be concealed under a few inches of fresh snow. Additionally, any avalanche could carry you over ground hazards and be traumatic. Use extra caution during these thin conditions. 

Please consider submitting an observation of what you see in the mountains. Even a simple photo helps forecasters better understand conditions and create more accurate forecasts.

Contact us here if you're interested in volunteering for a field day with the Avalanche Center. This is a unique opportunity to ski or ride with a forecaster and learn or grow your own snow and avalanche skills. 

Ski and ride safe!

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