Lawinenlagebericht

Swan Range

Flathead Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Blustery winds have drifted recent snowfall into slabs in unusual locations. Reduce your risk of triggering an avalanche by steering around wind-affected slopes. Buried weak layers can still be human-triggered, resulting in a large dangerous slide. Cold temperatures dictate a simple plan to ensure a minor incident does not develop into something worse.

Lawinenprobleme

  • Wind Slabs

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

    Two natural wind slab avalanches occurred yesterday in John F. Stevens Canyon. Observers reported active wind transport and new wind slab development in the Flathead and Swan Ranges. North and east wind speeds have tapered overnight, but slabs reactive to a rider's weight may be found in unusual locations on atypical aspects.  Due to the recent strong winds, slabs may be lower on the slope than expected. Continued cold weather is slowing the strengthening of these wind-formed features. 

    Slabs can be identified by the snow your traveling through becoming deeper or denser. Cracks shooting out from your skis or sled indicate that you've found an unstable slab. Think about what would happen to you if the slope you are on avalanches. This sobering thought should direct you to slopes free of surface obstacles which would minimize the consequences of a slide.

    (1/28/2023)

    Blowing snow from northeast winds.

    Photo: Dundas

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–3

    In the past week, riders have triggered avalanches on a buried layer of facets or surface hoar. Snowpits reveal that this weak snow is present in various locations and reactive in tests. This layer is found on shady aspects 1-3 feet below the surface in the Swan Range. Buried facets and surface hoar are slowly gaining strength, but recent snowfall and wind are testing this layer. The easiest way to manage this problem is through terrain selection. Continue to choose lower-angle terrain free of overhead hazards and convexities. Slopes with clean runouts are an excellent way to build a margin of safety into your day.

    (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

An arctic air mass crossed the Continental Divide Thursday morning and is now well entrenched throughout the Flathead Valley. Bitterly cold ambient air temperatures are reported this morning, with stations at all elevations below zero. Polebridge is the cold spot, with a temperature of -24 F at 0500. Despite a forecast of clear skies and plenty of sunshine, temperatures today will struggle to reach the single digits at mid and upper elevations.

Moderate to strong north and east winds accompanied the arrival of the arctic air. Wind speeds peaked Friday night into Saturday morning, with the Aeneas Ridge station (7186') reporting 13 consecutive hours of sustained winds greater than 40 mph with gusts above 60 mph. Wind speeds above 38 mph are classified as extreme and often called gale force. Fortunately, winds were diminishing and have decreased to a more tolerable level this morning.   

Following Friday's snowfall, the winds have been the driving force in avalanche danger. Wind slab has returned to the top of the problem list as these atypical winds form slabs in unusual locations. The amount of new snow available for transport varies widely across the area. The recent storm favored the Swan Range with 2 inches of SWE, while the Whitefish Range picked up less than 0.5 inches. We do not have an operating weather station in the Flathead Range, but observations point toward totals slightly more than what was recorded in the Whitefish Range.

In areas sheltered from the wind, sluffing in the surface snow is to be expected. The cold temperatures are faceting this snow and making it less cohesive and weaker. In some locations, this snow rests on a crust that inhibits bonding and allows sluffs to travel further than expected. This problem is confined to steep terrain, generally above 38 degrees, and is most dangerous in long-running gullies or lengthy sustained pitches. 

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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