Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Sun
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

Use small, low-consequence slopes to feel out new snow before committing to steeper terrain. The wind has stiffened the surface into sensitive drifts along ridgelines, saddles and gullies. Loose snow can slide fast and far on a firm crust.

Problemi valanghivi

  • Wind Slabs

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

    A pulse of moisture and gusty westerly winds is all it took to build slabs of wind-stiffened snow sensitive to human triggering. These can be found on upper-elevation leeward slopes particularly beneath ridgelines and along slope mid-slope ribs and gullies. These slabs are likely resting the widespread melt-freeze crust or weak, faceted surface snow, which could increase their sensitivity. 

    Blowing snow, textured surfaces, and dune-shaped features are all indicators of wind-drifted snow and cracking in the snow beneath you or your machine indicates an instability. Use small, inconsequential terrain to feel out the surface snow.  Consider adjusting your route if you encounter drifts that are particularly thick or wide where the slope is steep enough to slide.

  • Loose Dry

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

    New snow will sluff readily on steep slopes sheltered from the wind.  Slides will travel faster and further where snow fell on the recent melt-freeze crust. Small sluffs can still pose a risk if they knock you off your feet and send you over a cliff, through rocks and trees, or into a gulley - where even a little snow can bury you.  Use your imagination to consider the consequences of getting knocked off your line and adjust your route to lessen your exposure. 

    (2/28/2023)

    A thin, point release or Loose Dry sluff on a steep slope.

    Photo: sw

Avalanche Discussion

It’s hard to be disappointed when your expectations are low. I carried that attitude into the Swan Range yesterday (Friday) and was happy to find roughly 4-6” of new snow sitting atop an edgeable melt-freeze crust on most upper-elevation slopes. I saw blowing snow and found that gusty westerly winds had already formed isolated pockets that cracked easily underfoot along my ridge route. Small sluffs moved fast on steep, sheltered slopes.

This morning, weather stations suggest that my experience was about middle-of-the-road for the advisory area. Stations in the Whitefish Range, Flathead Range and southern Glacier National Park are showing 2-4” of new snow while Noisy Basin in the Swan Range managed to squeeze out 6” of snow and 0.6” of SWE. Westerly winds remain strong enough to continue transporting snow and building slabs. These will be largest in areas favored by recent snow and wind. With few weather stations and even fewer observations it’s difficult to determine exactly where that might be, outside of Noisy Basin. Pay attention to the amount of new snow during your travels today. If you find totals of 6 inches or more, you may need to adjust your route to reduce your risk. Steer around rippled surfaces or dunes along ridgelines, saddles, and mid-slope ribs and gullies. Choose slopes without terrain traps to lessen the consequences of a small slide. 

Though the stats on yesterday’s storm are far from impressive. Recall that even small loading events have produced large avalanches on buried weak layers this season in the central-northern Whitefish Range, Flathead Range and southern Glacier National Park. We’ve received no reports of avalanches failing in old snow from the Swan Range for over a month.

FOFAC Event: March 30th, 2023– Whether you're chasing tan lines, big lines, or both, you'll learn something valuable from FAC Lead Forecaster Mark Dundas about spring avalanche problems, how they differ from winter problems, and how to manage them. We will also discuss current conditions and concerns (or lack thereof!) with our spring snowpack. Enjoy a cold brew from Bias Brewing and a scoop from Sweet Peaks Ice Cream. The event is free and open to everyone. Begins at 6 pm.

 

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