Avalanche forecast

Swan Range

Flathead Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Shifting winds will drift new snow into slabs throughout the day. A surface slide has the potential to trigger a large avalanche on a buried weak layer. Expect changing conditions as the day progresses. Seek out sheltered terrain to limit exposure to fresh slabs and dangerous wind chills. Continue to be vigilant with slope angles by sticking to terrain less than 35 degrees. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    A poor snowpack structure exists on all aspects above roughly 5000 feet. New snow alone won’t be enough to overload weak layers buried 1 to 3 feet below the surface. The caveat would be a larger trigger, such as a person or a triggered avalanche in the new snow that steps down. The result would be a large, destructive avalanche taking out most of the season’s snowpack. Stick to slopes less than 35 degrees and steer around steep rollovers.

    (12/14/2022)

    Profile conducted 1.5 m from point where I triggered a large whumpf. This snowpack structure was consistent to 7300 ft on slopes with a similar aspect, though slab thickness varied and MFcr not always present.

    Photo: br

  • Wind Slabs

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

    Today's winds will easily transport recent and overnight low-density snowfall. Expect new slab development that will thicken as the day progresses. Look for blowing snow and a denser or stiffer surface as you gain elevation. Cracking beneath your feet or machine is a sign of instability, directing you to a different slope. A small slide in the drifted snow has the potential to trigger a much larger avalanche on a buried weak layer. Stick to sheltered terrain for a safer and more enjoyable experience.

    (11/28/2022)

    Shooting cracks were observed in locations harboring a cohesive surface slab. This slab rested on a layer of weak faceted snow which produced collapsing and whumphing.

    Photo: Mark Dundas

Avalanche Discussion

The well-advertised arctic air reached Marias Pass mid-morning Saturday and gradually made its way west. Concurrently, a mass of arctic air marched south over the International Border and down the North Fork of the Flathead. Bitterly cold temperatures and blustery north through-east winds accompanied these cold air pools. As of 0400 Sunday morning, dangerously cold ambient temperatures and wind chill readings are centered in the Essex to Marias Pass corridor, where all weather stations report below-zero temperatures. The Snowslip weather station (6950 feet) is the coldest spot at negative19 F.  Other cold spots include the northeast side of the Whitefish Range and central Glacier Park. Expect the cold air to deepen and eventually affect all of Flathead County through the work week.

Most weather stations in the valley floor and ridgetop locations report north-to-northeast winds with wind speeds varying from light to strong.  The exception is  Aeneas Ridge, WMR, and Sperry, where southwest winds remain. Eventually, these stations will shift north-to-northeast as the cold air strengthens its grip on the region.

Several inches of low-density snowfall on Saturday night add to the previous fluffy snow surface. Winds will easily transport this snow throughout the day onto atypical aspects. The exception will be in locations still holding onto the southwest flow. In those areas, expect loading onto slopes facing north through east until the winds shift. Forecasted snowfall through the day will add fuel to the fire and keep the wind transport machine well-oiled. 

North through east winds will form thin slabs of snow on sunny aspects at all elevations. These are the same slopes that hold the thinnest snow cover and have the weakest snow structure.  The potential exists for a surface slide in the wind-drifted snow to step down to a buried weak layer resulting in a large avalanche.  There is not a lot of water associated with today's storm, and we don't anticipate this new load to trigger these avalanches in areas sheltered from the wind.

We have rated the danger on the low end of the MODERATE scale for the past few days. Today's fresh snow and winds have bumped the danger to the upper end of the MODERATE hazard. Besides today's increasing avalanche danger, the cold air temperatures and brutal wind chill can turn a minor problem into a severe emergency. Keep your plan simple and short.

If you're joining us this season or need to play catch up, check out Sarah's weekly condition summary and video by toggling the tab above.

Training: Now's a great time to hone your companion rescue skills. Transceiver parks are open at Whitefish Mountain Resort, one at the summit and one adjacent to Grey Wolf. Both are accessible to snowmachines. Or check out our Motorized Companion Rescue Clinic on Sunday, December 18. You can get more details about training and education opportunities events on our events calendar.

Observations - Thanks to everyone who's been utilizing our new observation submission page. Try it out and help your community by sharing what you see in the backcountry. The form requires you to fill out the location fields and put a dot on a map. Be as specific or vague as you want. Our new Observation View page highlights signs of instability and allows you to filter by date or zone to pull out reports relevant to your objectives.

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