Bollettino valanghe

Flathead Range & Glacier NP

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

There remains a chance you could trigger a very large avalanche on a buried weak layer. Steer around steep roll-overs and areas where the snowpack is thinnest–like rocky, wind-scoured slopes. Move to wind-sheltered terrain if the snow surface cracks beneath you.

Problemi valanghivi

  • Persistent Slabs

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

    It’s been seven days since a very large avalanche failed on weak layers buried 2-4 feet deep in the Flathead Range. This slide fractured roughly 1500 feet across and ran an estimated 2500 vertical feet. Similar avalanches have been reported in the Flathead Range, southern Glacier Park, and the Whitefish Range since mid-February. These slides ran on aspects NW, through NE, to SE, and above 5000 feet in elevation. Recent avalanches are the most obvious sign of danger.  

    Although it is becoming more difficult for a rider to trigger an avalanche on buried weak layers, you can still stack the odds in your favor. Do this by digging into the snow to observe and test buried weak layers before committing to steep terrain. You can increase your safety margin by steering around likely trigger points, including wind-scoured or rocky areas–where the weak snow is closer to the surface–or steep roll-overs. Choosing slopes away from overhead hazards, limiting your time above terrain traps, and traveling one at a time in consequential terrain are easy ways to reduce exposure.

    (3/8/2023)

    The crown of a very large natural avalanche is visible in the upper left of the image, on the lee side of Grant Ridge (map name) on the crest of the Flathead Range. This slide likely ran during the natural avalanche cycle the last full week in February. 

    Photo: br

Avalanche Discussion

Today we’ll enjoy another day of generally stable conditions. I generally say this because evidence suggests that a Persistent Slab problem lingers in the Flathead Range, southern Glacier Park, and central to the northern Whitefish Range. 

The most recent reminder of this came yesterday (Wednesday) when Guy and I found a large hard slab avalanche on an upper-elevation Southeast aspect in the central Whitefish Range. This avalanche likely failed on a buried weak layer during a wind-loading event late last week. We ratcheted up our skepticism a notch and dug a pit on a northerly slope before committing to a steep climb on the same aspect. We did the same before descending a Southeast aspect and found a thinner and weaker snowpack that produced mixed results in snowpack tests. With this information, we elected to avoid likely trigger points as we descended one at a time.  

Observations from yesterday indicated light-blowing snow. With easterly winds increasing today, you might find isolated pockets of wind-drifted snow in unusual locations. Keep in mind that small surface slides have the potential to step down to buried weak layers and cause a larger avalanche.  Reports from the field also featured weak surface snow. Guy and I found a fresh and widespread crop of surface hoar in the central Whitefish. Cam found faceted surface snow in the Northern Swan.  Let us know what you find today, as an incoming storm will soon cover it. 

Thanks to Ted Steiner and Adam Clark with BNSF snow safety, as well as volunteer Tom Whipple for returning to the Tunnel Ridge weather station to replace the wind sensor.

Fireside/Snowpack postponed to Wednesday, March 15. Join us for a virtual evening combining two of our favorite community ed workshops: State of the Snowpack and Fireside Chats. FAC forecaster Cam Johnson will be presenting the State of the Snowpack to help you digest the conditions and plan your next trip. 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 a recent near miss. No registration is needed, click here for Zoom. Event will begin at 6 p.m. Thank you to the Whitefish Convention & Visitors Bureau for supporting our community engagement programs.

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