Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
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

Wednesday's blustery conditions formed large drifts of wind-blown snow reactive to the weight of a rider at middle and upper elevations. The hazard remains elevated where you encounter fresh, dense slabs on steep slopes near ridgelines, in gullies, and on cross-loaded features. Recent avalanches, cracking in the surface snow, and collapsing direct you to lower-angle or sheltered terrain free of overhead hazards. 

Problemi valanghivi

  • Wind Slabs

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

    The Swan Range received less precipitation than the other zones, but what it lacked in new snow, it made up for with moderate to strong winds and gale-force gusts (See Rob's video to the right or above).  Expect dense slabs of wind-blown snow resting on lower-density snow at middle and upper elevations. Due to the impressive wind speed, slabs may be farther down the slope than expected. Anticipate finding soft and hard slabs near ridgelines, gullies, and cross-loaded slopes. Hard slabs are particularly dangerous as they tend to support your weight and may not give any warning signs before breaking. There is the possibility that a surface slide could step down to a buried weak layer, resulting in a much larger avalanche. 

    Actively blowing snow, a rippled snow surface, dunes, and pillow-like features confirm that the wind has been at work. Cracking in the surface snow or whumpfing collapses confirms you have found an unstable slab. This problem can be avoided by choosing lower-angle terrain or slopes sheltered from the wind that will hold much softer snow. 

     

Avalanche Discussion

Wednesday’s heavy snow fell on a widespread layer of lighter, drier snow, resulting in an unstable upside-down surface. Moderate to strong winds transported the new snow into thick, dense slabs on leeward slopes. Observations are sparse, but we assume a natural avalanche cycle coincided with periods of intense precipitation. 

The warm, wet weather affected all zones and elevations but favored the Whitefish Range with storm totals of 1.3 inches of water at WMR, 1.5 inches at Stahl Peak, and central Glacier Park with 1.6 inches. The snow line climbed throughout the event, with mid-elevation stations reaching near or above freezing temperatures. Rain fell to or above 5500 feet on the Swan Front (image).

Cam was in the southern Whitefish Range, where he noted six soft slab avalanches failing on a density change 6-10 inches deep. He remotely triggered one slide and observed widespread cracking and several collapses. 

In the Swan, Rob observed intense wind loading from strong winds and gale-force gusts. Snowpit tests revealed hair trigger propagation beneath a recent crust 20cm down. 

Although the natural cycle has ended, it remains likely that a rider could trigger an avalanche in the fresh slab. We recommend giving the new and wind-blown snow additional time to strengthen before committing to steep terrain. 

Downloaded the app yet? You can now access our region's forecasts, observations, and weather data directly from the Avy App (IOS; Android). Many features are accessible offline, so you can doublecheck danger ratings and travel advice on the drive or in the backcountry. And submit an obs while driving home. 

Are you looking for avalanche education opportunities? Check out our calendar for upcoming events. A Partner Rescue Clinic for motorized Riders on January 4 would be a great way to start the new year.  

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