Lawinenlagebericht

Swan Range

Flathead Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Thin slabs of wind-drifted snow reactive to the weight of a rider remain today's primary hazard. A potent weather system will increase the avalanche danger overnight. Dangerous avalanche conditions may develop throughout Friday.

Lawinenprobleme

  • Wind Slabs

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

    Light southwesterly winds with moderate gusts across our region today will continue transporting the few inches of recent snow into thin wind slabs. You will encounter these features near ridgelines and in cross-loaded features like chutes or gullies. As you travel today, pay attention to changes in the snow’s density as a way to recognize wind-stiffened snow. If you observe cracking around your machine or skis, you are probably moving through a wind slab. Although relatively small, the consequences of a slide dragging you into a terrain trap could be severe. Monitor the snow surface for signs of wind transport and thicker drifts, as the next weather system brings increasing winds and snow later today.

    (1/17/2023)

    Blowing snow.

    Photo: Adam Clark

  • Persistent Slabs

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

    A thin layer of facets or surface hoar is found in a spotty pattern across the area. This layer is buried 1-3 feet below the surface and is responsible for a handful of triggered avalanches. Currently, this layer is unreactive, but the incoming storm may awaken this sleeping dragon. The weak layer is most dangerous in areas where a thick slab rests above. Choosing lower-angle terrain free of overhead hazards is a surefire way to avoid tangling with this problem.

    (1/21/2023)

    This small, but relatively thick avalanche was triggered remotely by a snowbiker. The rest of the slope cracked but did not slide.

Avalanche Discussion

Pacific moisture enters the Flathead this afternoon as the leading edge of a potent storm marches east. This system intensifies overnight Friday before exiting the region Saturday morning. Expect wide-ranging precipitation totals of 0.5-2.0 inches of SWE, with the Swan Range favored. Winds will ramp up from the southwest, increasing the avalanche danger overnight and throughout Friday. Dangerous avalanche conditions will develop. Bitter arctic air, accompanied by dangerously cold northeast winds, moves east across the Continental Divide Friday night through Tuesday.  

Yesterday (Wednesday), two forecast teams were in the field searching for evidence of our buried weak layer. As we’ve shared since listing the Persistent Slab problem on 1/18/2023, figuring out the distribution of this “spotty” layer has proven challenging. Building on what we know, we can add that both teams did not observe instabilities associated with the buried weak layer.

Observation Highlights from Wednesday:

  • Professional Observer-Guy and FOFAC’s Education Coordinator Meg toured the Northern Whitefish Range, catching a beautiful inversion day with lots of sunshine. When they searched and dug in the snowpack, rather than finding buried surface hoar, they discovered that the 3 to 5 inches of new snow resting on the stout, supportable MLK crust was evidence to enjoy skiing some steeper slopes.
  • Cam and his partner also did not find evidence of the buried weak layer in the Essex area of the Flathead Range. They climbed up to 7600 feet and were spooked by a south-facing slope that was shallow in snow depth, with large depth hoar crystals. Using that information, they chose not to ski that southern slope and instead chose a west-facing pitch with a hard, supportable crust that did not have evidence of a buried weak layer.

It is important to note that there is still uncertainty about the reactivity of the buried weak layer in the Swan Range. Additionally, the Swan Range is favored to receive higher snow accumulation totals from Friday’s incoming storm. The remotely triggered avalanche from last Saturday (1/21/23) in the Swan should still be considered a warning that we can not write off the potential for triggering an avalanche on a buried weak layer. 

 

Motorized Partner Rescue - Join us for an eight-hour field day on Saturday, January 28, 2023. More details are 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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