Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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

In sintesi

Dynamic springtime weather can rapidly change the avalanche hazard. As you travel in the mountains today, continue to monitor snowfall totals and changes in the snow density. You can reduce your risk of triggering a slide by choosing to ride lower angle slopes.

Problemi valanghivi

  • Wind Slabs

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

    Favored locations have received 4-8+ inches of new snow over the past two days. Southwesterly winds have been strong enough to drift snow and form slabs. Look for these features near exposed ridgelines and mid-slope gullies. As you climb in elevation, these slabs will be thicker and more widespread.

    In locations sheltered from the wind, you may encounter thin slabs in the newly fallen snow. These slabs will be more widespread and dangerous in areas with the most snow accumulation. 

    Both slab flavors will feel dense and may support your weight and your machine's weight. Cornices, dunes, and rippled snow are clues that the wind has been at work. Cracking around your feet or machine indicates that you have found a sensitive slab directing you to seek out less steep terrain. 

    (3/7/2024)

    Southwest winds have been strong enough to drift loose surface snow onto leeward aspects, as shown in this image of Nyack Mountain. 

    Photo: Mark Dundas

  • Loose Wet

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

    Spring weather is dynamic and should continue to be on your radar. Overnight snow, rain, and afternoon warming all contribute to wet snow instabilities.  Today’s dry snow transitioning to wet for the first time will be most unstable. You will likely see rollerballs and point releases in the new snow on steep slopes as your first warning signs.

    Be on the lookout for snow falling from tree branches or shedding off rock outcroppings as an indicator of the day’s warming. Triggered and natural rollerballs growing in size and distribution prove the surface snow is losing strength. These are all signs to seek out lower-angle terrain free of overhead hazards. Limit your time spent above terrain traps, where debris can pile up and push you into places you don't want to go.

    (4/5/2024)

    Today every aspect had fields of rollerballs. We suspect that increased wet loose activity occurred in the afternoon. We didn't stay around to watch it happen. 

    Photo: Sarah Williams

Avalanche Discussion

April showers, bring the powder. The Swan Range benefitted from yesterday's southwest flow, with Noisy Basin recording 12" of settled snow and 2.4" of SWE (Snow Water Equivalent) in the past 24 hours, 1.8" of which fell overnight! Stryker Peak in the Whitefish Range picked up 8" of settled snow and 1.3" of SWE with WMR in the southern part of the range recording 0.8" of water. The Flathead Range generally receives spillover moisture when Noisy gets slammed, but the solitary weather station in this range, Tunnel Ridge, only recorded a modest couple of inches. However, I would be shocked if other nearby drainages did not record decent snow totals.

Recent north and east winds backed to the west-southwest yesterday and increased in speed throughout the day before tapering overnight. The windiest station in Flathead County, Aeneas Ridge in the Swan Range, recorded seven consecutive hours of average speeds of over 20 mph with gusts in the 30s. Wind speeds of 16 mph or greater can generally transport snow. For those familiar with this area, wrap your mind around the bountiful wind loading in the steep east and northeasterly-facing chutes that drop off Aeneas Ridge into the Picnic Lakes area. 

Yesterday (Saturday), observers enjoyed a variety of weather and snow surface conditions. Rob and I rode in the central Whitefish Range, noting 4-6 inches of moist new snow and stubborn drifts to snowmobile traffic. As the day progressed, instability was limited to trees shedding snow, rollerballs at upper elevations, and an increase in boot/sled penetrations. A professional in Spider Bowl in the Swan found 6" of new snow had accumulated above yesterday's wet supportable surface and summed up their experience well: "If you like it damp, today was a good day to get out." A seasoned observer enjoyed 8" of soft snow in Canyon Creek in the southern Whitefish Range. As they descended in elevation and the slope angle reached the mid-30s, they found the increasingly heavy snow breaking at their feet and running.

Mark will issue FAC's last daily forecast tomorrow, Monday, April 8, 2024. After that, we will continue to write conditions updates on Tuesdays and Fridays until May 3 or as conditions dictate. 

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