Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Know where you are today - aspect? elevation? terrain above? - so you can adjust your travel to a suite of lingering avalanche concerns. The hazards threatening your approach will likely be different than those existing at your objective. And by the time you exit, the danger posed by wet snow avalanches may have increased. These hazards involve the surface and near surface layers of the snowpack and can be large enough to bury or injure a person.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Below about 6000 feet, you can trigger wet snow avalanches that can be dangerous above terrain traps. These conditions will be most common on shaded slopes where the surface snow is changing from dry to wet. They're also possible on very steep slopes where crusts have softened. Avoid being on or below slopes steeper than about 40 degrees where you find fresh rollerballs or sticky snow clumping to the bottom of your board, skis, or machine. 

    (2/9/2022)

    Rollerballs are one of the first signs that snow is becoming wet and likely to start sliding downhill

    Photo: Tom Whipple

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Be alert for whumping collapses and shooting cracks. They're announcements that you've found an area where you can still trigger avalanches that fail on collapsible layers of surface hoar and facets near crusts. While these layers are widespread across the forecast region, riders have only reported triggering avalanches breaking on these layers in the southern Whitefish Range. Sadly, the slopes most likely to harbor this hazard are also those most likely to harbor cold, dry snow: steep, shaded, wind-sheltered slopes at mid and upper elevations. Stack the deck in your favor by riding planar or concave slopes with clean runouts - no gullies, trees, or rocks below.

    (2/7/2022)

     A rider stomped along a cornice/rollover and set off a decent sized slide, 6-12" crown, approx 100' wide. North-northeast aspect, 6380 feet in the Southern Whitefish Range on 2/7 

    Photo: Public

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–2

    Recently-formed slabs of drifted snow pose a lingering hazard at upper elevations. These can be triggered by falling cornices, which are weakening in the warming weather. A person may still be able to trigger them from thin spots near rocks, from their edges, or from below, as you're climbing towards a ridgeline. Avoid traveling below corniced ridges, and be cautious before climbing or dropping into the tops of steep chutes and cross-loaded gullies.

    (2/9/2022)

    These mid-slope avalanches pulled out as a large, cornice triggered, slide came down on 2/5

    Photo: Alan Davis

Avalanche Discussion

Warm, windy weather is shuffling our avalanche concerns, with wet snow avalanches a growing hazard after a second night with a brief or no refreeze. Meanwhile, concern about the Persistent Slab avalanche problem is diminishing as the upper snowpack settles and consolidates. Wind slabs remain an isolated hazard, because the wind-slab machine has exhausted its supply of soft, transportable snow and existing slabs have had time to stabilize.

With 24 hours or more of above freezing temperatures at mid elevations, wet snow avalanches are becoming a hazard in this elevation band. Slopes where the snow is getting wet for the first time will be the most likely place to encounter this hazard. You can tell you've found it if you have to clean sticky snow clumping to skis, boards, or machines, as a party reported from the Middle Fork Wednesday. This hazard is less widespread on slopes where melt-freeze snow remains refrozen. This hazard will spike on any slopes that receive sustained sun. 

The likelihood of triggering a slab on a shallowly-buried persistent weak layer is diminishing. While you can find surface hoar or facets buried six to 18 inches deep across the forecast region, the only reported slides that broke on these layers have been confined to the southern Whitefish Range. Specifically, to steep, north-, northeast-, and east-facing slopes east of Whitefish Mountain Resort. These layers are close enough to the snow surface that the warm temperatures are stabilizing them. But that's a slow process, so continue to be suspicious of terrain with possible trigger points and runouts with terrain traps. 

Warming temperatures are also weakening cornices, and as the cornices sag, they're more likely to break and drop. The falling debris can pose a hazard in itself, and it can trigger slabs of drifted slabs on slopes below. We've had several observations of large slides failing this way in the past few days. Keep an eye on the terrain overhead, and keep in mind that falling corncies and slides they triggered can run further than expected.

Tuesday morning, a freezing rain crust was deposited in the southern Whitefish Range. Riders reported a rime crust in parts of the Flathead Range. It's not clear yet how widespread these layers are.

Regioni coperte