Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Avalanches may still fail at a weak layer buried a few inches above a very hard crust. Overnight winds and a few inches of snow have formed thin pockets of wind drifted snow below ridgelines. Low angle slopes that are protected from the wind will be the most enjoyable today.  

 

Problemi valanghivi

  • Persistent Slabs

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

    A weak layer of facets has been the culprit in a series of accidents and near-misses the past four days. This layer is buried 12 to 24 inches deep, and sits 1 to 6 inches above a very hard crust. Moderate temperatures are helping this weak layer to sinter and gain strength. The rate will vary by slope, so you may find the structure present and unreactive in stability tests at one site, yet move several yards away and get a completely different result. This layer remained sensitive to the weight of a rider two days ago (Monday) in the Flathead Range. 

    Give steep shaded slopes above 6,500 feet plenty of room today. Choose slopes with runouts clear of trees and gullies. If you find yourself feeling the snow getting warmer and stiffening this afternoon, dial back your terrain selection and retreat to lower slope angles. 

    (2/19/2024)

    This photo paints a picture of where the current Persistent Slab avalanche problem exists. The shaded aspect, upper left, has a triggered slab avalanche on it. This is where facets became more developed during periods of high-pressure. The solar aspect, right side, has minimal rollerball activity and no slab avalanches. This is where the sun cooked weak layers before they were buried. 

    Photo: Cam Johnson

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Fresh snow and overnight winds have drifted snow near ridgelines.  Thin windslabs may sit atop several feet of old snow that has buried a weak layer.  If these break they can propagate much further across the slope than you expect.  Manage this by keeping to slopes that are planar and runouts that are clear of terrain traps.

    Wind affected snow just has "that look".  We all can see the texture change long before our skis or machine make contact with snow like this.  If you find yourself on a slope with snow that looks like this, make sure you are well away from any convexities and terrain traps that are below you.Photo: Joshua McElrath

Avalanche Discussion

Patience is the name of the game with today’s problems.  A Persistent Slab avalanche  structure exists across the forecast region. The primary concern is a layer of weak, faceted snow buried 12 to 24 inches below the surface and a few inches above the early February crust/ ice layer. The layer appears most developed in the Flathead Range, where slabs have been  reactive to the weight of skiers multiple times over the last 4 days (here and here). Several of these slides have been triggered from spots where the slab is thinner. The same facet and crust combo has been reported in the Whitefish and Swan Ranges. However, we’re not getting any reports of triggered avalanches in these 2 ranges. In the Flathead Range incidents, the parties observed no collapsing or cracking prior to triggering the slides. The take home message is that this weak layer may provide very little feedback, until it is breaking underneath you or your machine.  

Temperatures hovering around freezing and cloudy skies this morning mean conditions ought to be ripe for traveling on your favorite ridgeline today or riding from one drainage to the next.  If the sun does break through, or if the temperature exceeds the forecast, beware of loose snow avalanches.  Clues will be rollerballs and sticky skins. The Flathead Range has seen most south aspects get cooked lately. The Northern Whitefish and Swan ranges still harbor soft snow that hasn't been affected by the sun. This slight warming could also speed settlement and consolidation of the slab above the facets. Find small test slopes and terrain free of hazards below before commiting to a line if you feel this happening.  We have yet to see the facet/crust combo in the Whitefish and Swan Ranges tested like in the Flathead Range. 

 

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