Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Fri
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

New snow and wind will build drifts throughout the day. Be prepared to change your plans, back away from steep terrain, or adapt to increasing hazards with weather conditions.

Problemi valanghivi

  • Wind Slabs

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

    Moderate to strong southwest winds are expected to increase throughout the day. Fresh snow from earlier this week and today will be available for transport. Winds will drift new snow into leeward terrain on NW-S-SE aspects.

    Blowing snow will be an easy way to spot the problem as it develops today. Look for pillows or dune-shaped features near ridgelines, cross-loaded gullies, or around prominent terrain features. Although these slabs may be small this morning, they will continue to thicken through the day. While choosing terrain, think of the consequences of being knocked off your feet, dragged into a tree, or pushed over rocks. You can avoid the problem by choosing terrain where the snow is sheltered or being scoured by the wind.

    (2/16/2023)

    Recent snowfall was readily blown around at upper elevations from southwest winds.

    Photo: md

  • Persistent Slabs

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

    Numerous large to very large avalanches failed over a week ago (February 20th/21st) on buried weak layers. Getting caught in many of those slides would have been unsurvivable. Depending on elevation, these layers are generally buried 2 to 4 feet below the surface and most developed on NW-NE-SE aspects. 

    It is becoming more difficult for the weight of a rider or their snowmachine to trigger one of these slides. This is becoming a low probability - high consequence situation. Digging down to see if these layers are present is the best way to identify these layers. Remember that typical snowpack tests may not be effective in testing their strength. Choose lower-angle slopes free of overhead hazards. Steer around convexities and thin windswept or rocky areas where your weight is most likely to impact these layers.

    (2/25/2023)

    A very large hard slab avalanche on a wind-loaded slope.

Avalanche Discussion

Today the forecast calls for snow showers followed by a cold front this afternoon. West winds are anticipated to ramp up as the cooler airmass moves into the Flathead. This is a recipe for a building Wind Slab problem to develop this afternoon and possibly overnight. Monitor ridgeline winds and new snow as you travel in the mountains today. 

The predicted precipitation of Thursday into Friday will continue to bury weak layers of snow within the snowpack. We anticipate observing fewer signs of instability associated with our Persistent Slab problem. We’ve decreased the avalanche hazard to UNLIKELY for our Persistent Slab problem in the Swan Range and the Whitefish Range. Both the time span since the last loading event and the increased burial depth of weak layers increases the difficulty for a skier or rider to trigger a Persistent Slab avalanche. We have kept the likelihood of triggering at POSSIBLE in the Flathead Range.

Given the forecast and variability of weather conditions throughout the Flathead, keep in mind that the variability of snow conditions can surprise the best of us. To illustrate this, check out these observations of neighboring drainages in the Flathead Range that had different outcomes (avalanches) on similar aspects (observation, observation, observation, observation, & observation).

State of the Snowpack and Fireside Chats. Join us at 6 pm on March 9 for a virtual evening combining two of our 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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