Avalanche forecast

Swan Range

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Look for and steer around dunes of drifted snow in unusual locations.  You can trigger small loose snow avalanches on steep slopes that are sheltered from the wind.  Small slides have the potential to trigger a large avalanche on buried weak layers. Avoid travel on steep slopes and over terrain traps. Extreme cold will complicate any incident.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Winds shifted from our typical southwest flow to a north or east direction yesterday morning. Speeds increased overnight, with strong to extreme gusts common. Recent fresh snow is being transported into slabs in unusual locations and possibly further down the slope than expected. Today, slabs may be reactive to the weight of a rider in all aspects. Blowing snow will clue you into where the slabs are freshest. Encountering deeper and stiffer snow is a clue you've located wind-affected snow. Cracking in the snow surface is a sign of instability, directing you to seek out sheltered terrain or lower-angle slopes. 

    (1/7/2023)

    Prevailing winds scour and strip this face of snow. A thin row of trees acts as a wind fence, slowing down the wind, interrupting the flow, and creating eddies where deposition occurs.

    Photo: Mark Dundas

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    In the past week, riders have triggered avalanches on a buried layer of facets or surface hoar. This layer is found on shady aspects 2-4 feet below the surface in the Swan Range. Recent snowfall and wind are thickening the slab on top of this weak snow and possibly tipping the balance toward an avalanche. This is a tricky problem to navigate with terrain selection, your best bet for a successful day. 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

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    Observations from the Swan and Flathead Ranges yesterday (Friday) featured reports of small but reactive sluffs in the new snow.  You will most likely trigger sluffs in steep, sheltered terrain where the snow remains loose and dry. These slides can travel faster and further on hard crusts below that can sweep you off your feet, over a cliff, or into a terrain trap. Do your partner a favor, and avoid riding above them.

Avalanche Discussion

First, the snow, now the blow. Yesterday's storm has passed, but danger remains.  Snowfall shut down across the advisory area with the exception of some lingering flurries along the continental divide.  The Swan Range was favored, with Noisy Basin reporting 1.9” SWE.  The Flathead and Southern Glacier Park were distant runner-ups with 0.9” SWE at Flattop, while the Whitefish Range saw roughly 0.4” SWE at WMR and Stahl Peak. 

The recently-fallen snow will be easily re-distributed by ramping winds from Northerly to Easterly.  Mt. Aeneas in the Swan range saw winds crank up to 40 mph overnight, with gusts reaching 80 mph. This trend will build new and sensitive wind slabs in areas that are typically sheltered from our prevailing south-westerlies.  Don’t be surprised if you come across wind-drifted snow in unusual locations.  You can anticipate sluffing on steep slopes where the new snow isn’t impacted by wind.  This will be more prevalent in the Swan and Flathead ranges due to higher snow totals from the recent storm.  

Snow and wind aren’t your only concerns today. Remember, buried facets and surface hoar still lurk under the surface.  Furthermore, these weak layers are likely still adjusting to the load from new and wind-drifted snow.  Following our previous loading event last Saturday, we saw clear signs of instability in the Swan Range. This included shooting cracks and a remotely triggered avalanche.  Re-evaluate your objectives and move away from steep slopes if you encounter similar activity today.  In the absence of direct feedback, you can fall back on structure.  Dig down and look to see if you have a cohesive slab resting on top of weak faceted snow or surface hoar. Rule out slopes steeper than 30 degrees where you find this structure. Although much of our focus has been on the Swan, realize that we are still building slabs in the rest of the advisory area, albeit at a slower pace. 

Expect the avalanche hazard to wane over the weekend amidst dry conditions and tapering winds.  However, you can supplement that hazard with that of extreme cold through Monday.  Maintain wide safety margins so you don’t spend a frigid night in the mountains or worse.

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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