Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

An Avalanche Warning is in effect in all zones of our advisory area. Very dangerous avalanche conditions exist today, and will likely continue during a period of prolonged warming. Avoid traveling in avalanche terrain today.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Avoid traveling in avalanche terrain today. The likelihood of spontaneous large and very large avalanches makes steep terrain and avalanche runouts very dangerous today. Heat and radiation are destabilizing hard slabs perched on deeply buried weak layers. These layers are widespread but variable in strength, making it difficult to impossible to determine which slopes will fail and when. Debris from these slides can run the full length of avalanche paths. You are unlikely to survive getting hit by one of these beasts. The usual tests and terrain management practices are woefully inadequate in these conditions.

    (3/15/2024)

    Several hard slab avalanches ran naturally between 7500'-8500' on SW aspects. Possibly triggered by loose wet.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–3

    Overnight temperatures stayed above freezing at many mid- and upper-elevation stations, and today’s temperatures will climb higher than the past few days. Wet snow avalanche hazards will become more widespread and destructive, and they may include shaded aspects that have previously held dry snow. 

    Pinwheels or rollerballs indicate the snow surface is softening, and loose snow avalanches may soon follow. Avoid exposing yourself to this problem in terrain with overhead hazards. Avoid traveling above terrain traps, where debris can pile up deep, and in long-running gullies, where escape may be difficult.

    (3/15/2024)

    Several hundred feet of the popular Skook skin track was covered in rollerballs from the March 14 warming. 

    Photo: Mark Dundas

  • Cornices

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

    Impressive southwest winds built large cornices along alpine ridgelines in late February/early March. Intense warming this weekend is weakening these features. A failing cornice can send large blocks of snow trundling downhill. These can be dangerous in themselves. They can also trigger destructive avalanches that fail on deeply buried weak layers. 

    The nature of this problem is highly unpredictable and should warrant your respect. Give these whales a wide berth above and below a corniced ridgeline to reduce your risk. Don’t get surprised by a cornice breaking further back than expected.

    (3/7/2024)

    Cornices like these will begin to weaken, crack, and fall due to warming temperatures.  Do not linger on or under slopes with cornice looming overhead. Give them a wide berth as you navigate ridgelines. 

Avalanche Discussion

Ready or not, the heat is on for this weekend. We have issued an Avalanche Warning for the Swan Range, the Whitefish Range, the Flathead Range, and parts of Glacier National Park from 6 am today through 6 am tomorrow (Sunday). Remote weather stations have recorded above-freezing temperatures since yesterday, creating a lack of refreezing overnight. Heat and radiation destabilize thick, hard slabs, weaken cornices, and create widespread areas of wet surface snow.

We are most concerned about hard slab avalanches failing on buried weak layers. This Persistent Slab problem is unpredictable, and the consequences of getting caught in this type of slide are deadly. Observations from yesterday (Friday) included the BNSF Avalanche Safety Team’s report of 3 large slab avalanches observed from Highway 2. FAC Forecaster Cam observed a D2.5 hard slab avalanche on a northwest aspect of Great Northern. Outside of our forecast region, Rob, FAC Forecaster, viewed several large slab avalanches on the west, southwest, and south aspects of the Swan Crest.  These slides likely failed in the late afternoon yesterday. 

Natural and triggered avalanches involving wet surface snow are very likely on both sunny and shady slopes. We expect widespread wet loose activity today. Additionally, this heat wave will weaken ridgeline cornices and increase the likelihood of them unexpectedly breaking and subsequently triggering large to very large avalanches on the slopes below.  Planning an early exit and choosing low-angle terrain are ways to manage your risk in the face of uncertainty. If you observe avalanche activity, let us know what you are seeing by submitting an observation.

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