Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
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

You can trigger a slide where the wind has formed sensitive snow drifts. Look for these along ridgelines, saddles, and gullies. Steer toward wind-sheltered or less steep terrain if the snow cracks beneath your feet or machine.

Problemi valanghivi

  • Wind Slabs

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

    Blowing snow is an obvious indication of active wind-loading. West winds are drifting recent snow onto leeward terrain facing NW-through NE-to SE. Yesterday (Thursday), riders indicated that small pockets of wind-drifted snow became sensitive throughout the day. Today, slabs will continue to thicken. You'll find the biggest and baddest of these near ridgelines, in cross-loaded gullies, or around prominent terrain features.

    Steer around rippled snow surfaces and dune-shaped features, or increase your safety margin by choosing terrain where the snow is sheltered from or scoured by wind. The current conditions are adding to the size of cornices. Don't linger below cornices as they may fail naturally, and give them a wide berth as you traverse ridgelines.

  • Persistent Slabs

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

    Numerous large to very large avalanches ran during last week's atmospheric river and wind-loading events. These slides failed on buried weak layers, and many would have been unsurvivable for a rider. These layers are generally buried 2 to 4 feet below the surface, depending on elevation. The structure appears to be weakest on aspects NW-through NE-to SE. 

    It is becoming more difficult for the weight of a rider or their snowmachine to trigger one of these slides. A collapsing cornice or small avalanche, however, might do the trick. Digging into the snowpack is the best way to identify these layers. Remember that typical snowpack tests are not always reliable when testing their strength. Steer around convexities and thin windswept or rocky areas where your weight is most likely to impact these layers. Choose lower-angle slopes away from overhead hazards to increase your safety margin further.

    (2/25/2023)

    A hard slab avalanche on a mid-elevation northeast aspect on Nyack Mountain.

    Photo: md

Avalanche Discussion

Observations from yesterday (Thursday) were snowglobe-esque. My partner and I were shaken particularly violently by gusts approaching extreme. We elected to abandon our objective and sail out of the avalanche terrain. In all cases, riders indicated a developing wind slab problem. Today, the wind slab machine rages on. Though slightly less impressive, light snowfall and wind will thicken slabs and build sensitive cornices.  

Wind slabs will be larger, more sensitive, and easier to find in areas favored by the recent wind. Weather stations at Hornet and Aeneas Ridge recorded gusts of approximately 60 mph with sustained wind speeds ideal for transporting snow. The large bowls of the northern Flathead Range or along the Continental Divide also come to mind. Be attentive to the extent of wind-affected surfaces and rethink your route if the problem becomes too widespread to manage. 

If you succeed in avoiding the wind today, recognize that the new snow may sluff readily on steep, sheltered slopes. Consider where you might end up if swept off your feet, and avoid skiing above your partner.

State of the Snowpack and Fireside Chats. Join us at 6 pm on March 9 for a virtual evening combining two popular community ed workshops. New this season, State of the Snowpack is a presentation from FAC on recent weather and avalanches to help you digest the forecast and plan your weekend. Fireside Chats are an intimate, conversational forum for open dialogue about human and avalanche factors. With skier/psychologist Dr. Sara Boilen as our facilitator, we dig into the tough decisions, tricky snow, and lessons learned from local near misses. No registration is needed; click here for a Zoom invite.

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