Bollettino valanghe

Whitefish Range

Flathead Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

You could trigger a large avalanche on buried weak layers on slopes shaded from the sun. New snow may slide readily on steep slopes. Pay attention to hazards above and connected to the slopes you travel on.

Problemi valanghivi

  • Persistent Slabs

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

    Numerous large to very large avalanches failed a week ago (February 20th/21st) on buried weak layers. Getting caught in many of those slides would have been unsurvivable. The majority of the avalanches occurred on shaded aspects at mid and upper elevations where the weak layers are most developed. Depending on elevation, these layers are generally buried 2 to 4 feet below the surface. 

    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 a chore, and 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

Despite the Whitefish Range being favored for yesterday’s storm, Noisy Basin (Swan Range) received the most new snow with 8 inches within 24 hours and adding 1 inch of SWE.  The Tunnel Ridge (Flathead Range) weather station picked up 7 inches of new snow and the Big Mountain (Whitefish Range) weather station gained 4 inches of snow.  If the new snow stays cohesionless, managing a loose dry avalanche problem will be expected today. The forecast calls for similar snow squalls throughout the day, so continue to monitor new snow totals as you travel.  

A widespread avalanche cycle occurred in the Flathead Range last week as the result of an atmospheric river. Here are a few noteworthy avalanche observations (observation, observation, observation). One observer noted that the recent avalanche activity around Marias Pass looked like “spring action,” despite the recent Arctic air mass of the past week. This is interesting, as we enter the month of March, with 19 days until the official start of Spring. Although we’ve received fewer observations from the Swan and Whitefish Ranges, it appears that these zones did not have as widespread of natural avalanche cycles (observation). 

Weak layers of snow exist throughout the advisory area. These layers produced large and very large avalanches last week. We are in a period where signs of instability are inconsistent and becoming less common. Both time since the last loading event and an increased burial depth of weak layers increase the difficulty for a human to trigger an avalanche. Tracks on a slope do not indicate that the slope is safe. Slabs, especially where they are hardened by wind, can break far above you and be nearly impossible to escape. The Persistent Slab problem is trending toward becoming unlikely to trigger.

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 Zoom invite.

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