Bollettino valanghe

Whitefish Range

Flathead Avalanche Center
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Pericolo valanghe

Sun
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Plan your route to steer around areas where the snowpack is thin and rocky. It’s unlikely–but not impossible–that you will trigger a large avalanche. New and wind-drifted snow have added stress to buried weak layers.

Problemi valanghivi

  • Persistent Slabs

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

    New and wind-drifted snow has added a modest load to buried weak layers. Previous unassuming loading events still produced isolated natural avalanches large enough to destroy a wood frame house.  Slides failing on weak layers have been confined to aspects NW-NE-SE this season.

    Weak layers are generally buried at a depth that a rider is unlikely to affect, but thin spots in the snowpack remain potential trigger points for backcountry riders. This concept is supported by last week's - potentially goat triggered - avalanche on Red Crow Mountain, just outside the advisory area (Photo above/right).  Small surface slides or cornices have more mass than a human or machine and can still affect buried weak layers even where the snowpack is deepest.  On Wednesday, Cam and Guy deliberately broke off a piece of cornice, triggering a slide on a buried weak layer in the central Whitefish Range.

    Use one or more of the following methods to reduce your exposure to this hazard:

    • Choose slopes with a uniform and deep snowpack
    • Steer around likely trigger points including convexities or slopes speckled with rocks
    • Choose simple or lower angle terrain

    (3/22/2023)

    The crown of a hard slab avalanche that may have been triggered by goats in southern Glacier Park, east of Marias Pass. This crown has been partially filled in from wind-loading.

    Photo: Tyler Lucas

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 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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