Lawinenlagebericht

Silver Valley & Bitterroot Mountains

Idaho Panhandle 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 2 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Recently, upper snowpack layers settled into a stiff, stubborn slab, but one that still sits above concerning weak snow layers. As fresh slabs of snow increase in depth, they are emerging as an avalanche hazard to manage and avoid. Adding a fresh slab on top of our stiff-over-soft combination is not expected to drive an immediate uptick in natural activity, but slides in the new snow could be the extra nudge required to provoke a deeper, more dangerous slide. With several snowpack questions still unanswered, maintain a conservative travel mindset near slopes steeper than about 30 degrees.

Lawinenprobleme

  • Persistent Slabs

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

    Weak layers buried a couple feet deep are the culprit of recent instability in the upper snowpack, with the most reactive slopes found near the tree line down to about 5,000 feet. Buried surface hoar is still the most well-preserved on north to east-facing slopes, while sunnier aspects have a breakable crust with faceted grains looming above and below it. Although deeper weak grains are showing initial signs of strengthening, they still remain vulnerable to failure if impacted from the "not-so-sweet" spot on a slope.

    We've struggled to paint a common sense pattern of weak layer distribution across aspects/ elevations within our forecast zones. Given the slab depth above these layers, triggering an avalanche could result in a large, wide-breaking, and dangerous slide. Backcountry users are still reporting warning signs like collapsing and cracking, though avalanche activity has diminished significantly. Our persistent problem is steady as she sails for now, but slab depth appears to directly influence triggering potential and ultimate avalanche size.

    (2/2/2025)

    Surface hoar visible at the bed surface of a human-triggered slide on a north-facing slope at 6,300 feet. Slab depth ranged 16 to 24 inches. Selkirk Mountains. February 2, 2025.

    Photo: Chris Bilbrey

  • Storm Slabs

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

    Snowfall since February 14 ranges 5 to 11 inches across the Bitterroot Mountains - Silver Valley. So far, recent snowfall has arrived with minimal wind and cold temperatures laying down a pile of goose down feathers. As the snowy period progresses over the coming days, temperatures are forecast to warm and this will likely form an inverted slab. As this happens, human and rider triggering will likely increase so watch for cracking in the snow as a sign the new snow is getting slabby. Steeper slopes with fresh slabs around a foot deep will be the most dangerous.

    Disturbing a pile of loose, unconsolidated snow in steep, open wind-sheltered terrain increases the chance for the new snow to sluff downhill. These generally harmless slides can pick up steam real quick and entrain additional snow volume. This poses the greatest risk if you get knocked off your feet above a cliff or pushed into natural obstacles, or stuffed in a terrain trap.

    (2/8/2025) Soft slab released just below a road cut.

Avalanche Discussion

Manage today’s storm snow hazard and you’ll likely avoid the sleeping dragon deeper within. Snow totals since February 14 are adding up nicely and will continue to stack up over the next 24 to 48 hours. Cold temperatures and light winds are helping the snow fall straight down and you’re more likely to find a pile of goose down feathers than widespread cohesive slabs. As you move closer to the treeline and above, you may start to encounter more wind-drifted, slabby conditions and where terrain management needs to change. Lens-shaped pillows, fresh cornice growth, or cracking in the snow will help clue you into the more dangerous places and where to go around.

Since the early-February storm cycle that drove a fast uptick in avalanche conditions following three weeks of high pressure, and one that lasted almost two weeks in time, the snowpack has now found a bit of balance. All of our persistent weak grain worries didn’t dramatically go away, they simply got more difficult to spark a failure and ensuing avalanche. Dangerous avalanches are still a potential in a steep, rocky, shallower area, or where the overlying slab is thinner from terrain twists, turns, or bends. Additionally, choosing to travel on slopes closer to 35 degrees also increases your chance to find trouble - more likely from a Storm Slab avalanche instigating a deeper failure.

Although natural and human triggered activity has significantly waned, warning signs continue to rear their heads - albeit less frequently. With how weak and advanced our primary layers of concern were before burial, chances are they will remain in a vulnerable state longer before quieting down or going away completely. If making a decision about stability is too challenging or you observe non-conclusive results in your evaluations, there’s plenty of excellent riding conditions on lower-angled terrain away from bigger avalanche terrain to wait for another day.

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