Lawinenlagebericht

Swan Range

Flathead Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
2 · Mässig
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Kernpunkte

07: 40 UPDATE: Due to an overproducing storm we have increased the avalanche danger in the Swan Range to HIGH and have issued an AVALANCHE WARNING. Fresh slabs may be found in sheltered locations and areas open to the wind. A surface slide has the potential to trigger a larger, more dangerous avalanche on a buried weak layer.  Stick to slopes less than about 30 degrees in steepness, free of overhead hazards. Travel in avalanche terrain is not recommended.

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    1–2

    Today's developing storm has deposited 0.8 inches of SWE at the Noisy Basin (6040') SNOTEL in the Swan Range as of 0500 this morning. This number should continue to climb as the day progresses. A slab can be identified as an area harboring deeper and denser snow. Cracking at the snow surface is a sign of instability, directing you to a lower-angle slope free of overhead hazards. An avalanche triggered in today's fresh snow may step down to a buried weak layer (Problem #2), resulting in a much larger slide.

    Steep slopes with 8 inches or more of loose dry snow may sluff naturally or be triggered by a rider. Manage your sluff and limit time above terrain traps where the snow can pile up deep.

     

    (12/24/2022)

    Drty soft slab (F+ hard) present in the morning at low elevations. The slab was about 50 cm of the recent storm snow; it was breaking on a 1cm weak layer - maybe small near-surface facets or surface hoar. 

    Photo: br

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    The Swan Range harbors a thin layer of facets or surface hoar on shaded slopes NW-NE-SE at mid and upper elevations. This layer is buried 1-4 feet below the surface and is responsible for several recently triggered avalanches. Today's storm will test slopes with this buried weak layer. The weak layer is most dangerous in areas where a thick slab rests above. Choosing lower-angle terrain free of overhead hazards is the best way to deal with this unpredictable problem.

    (1/26/2023) Northern Swan, Elev 6300', NE aspect, HS=153cm Buried SHsu observed on the underside of CT19 fracture on MLK crust. This layer did not propagate ECTN21

Avalanche Discussion

The well-advertised storm arrived a little later than expected this morning with slightly less punch than initially forecast for the Flathead. This storm impacts the Rockies from Steamboat, Colorado, to the Canadian border. The epicenter of snowfall in Montana as of 0300 is the Rattlesnake Mountains outside Missoula, where 1.3 inches of SWE fell in 9 hours. The Swan Range is favored in our area, with about an inch of SWE expected by Saturday morning. Update: As of 0600, Noisy Basin has recorded 1.0 inches of SWE in the past 6 hours. The Flathead Range may pick up around one-half inch of SWE, with slightly lesser amounts for the Whitefish Range. 

Due to intense precipitation rates this morning, we have issued an AVALANCHE WARNING for the Swan Range. The avalanche danger rating has risen in the other zones to account for the new snow and wind. The rating is based on snow totals panning out as forecast. Areas receiving higher than forecast snow amounts may become more dangerous than anticipated. We have added the storm slab problem to the Swan Range due to the amount of new snow expected.

Southwest winds increased overnight but will shift to a northern component as the day progresses. We have painted the wind slab rose on all aspects on mid and upper elevations to account for developing slabs on atypical aspects in the Flathead Range, southern Glacier Park, and the Whitefish Range.

The new load will stress buried weak layers, especially in the Swan, where the Persistent Slab problem is most well developed. We have unverified reports of multiple human-triggered avalanches on Thursday in the Swan Range. We are still seeking more information regarding these slides.  

Arctic air is still on track to cross the Continental Divide tonight and march west into the Flathead Valley. These cold air masses generally bring cold ambient air temperatures, gusty north through-east winds, and brutal wind chills. Unfortunately, they can shut down the precipitation under the right atmospheric circumstances. Think of this air mass as a big wall moving west that the pacific moisture can not penetrate. The timing of this arctic intrusion will determine if and when the precipitation is shunted.

Come one, come all! Flathead Avalanche Friends Fest, a four-day festival from Feb 8-11, has a full schedule with mini-clinics, a keynote speaker, après, and a Big-A$$ Raffle. A little something for everyone. We hope you can join us to celebrate our community, learn about snow, and support our safety mission. Learn more here.

Motorized Level 1 - Instructed by Eric Knoff and Six Points Avalanche Education from Tuesday, February 7, 2023, to Thursday, February 9, 2023. More details are here.

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