Avalanche forecast

Swan Range

Flathead Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

Sheltered terrain is where you will find powder riding and skiing. Varying generations of wind-drifted snow may still be reactive to human weight. Continue to monitor changes in the snow surface as you travel through different aspects and gain elevation. 

Avalanche problems

  • Wind Slabs

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

    North and east winds strong enough to transport snow have buffeted our area for the past 36 hours. Speeds are tapering this morning but still capable of forming slabs and cornices in locations favored by these atypical winds. These features may develop on a firm sliding surface such as a sun crust or previously scoured slope, adding to their instability. Older slabs formed from intense southwest winds Thursday and Friday are lurking on the opposite side of the compass. Today, expect to find a patchwork of soft and stiff features in all aspects. At lower elevations, north and east winds are notorious for wreaking havoc on and just above the valley floor. 

    If the snow you are moving through becomes deeper and denser, you are likely moving through a wind slab. Snowpack collapsing or cracks shooting out from your skis or sled indicate you are traveling on an unstable slab.

    Riders report excellent snow on slopes sheltered from the wind and sun. Seek out these areas for a safer and higher quality experience.

     

    (3/4/2023)

    A wind slab avalanche (top of photo) triggered a very large hard slab avalanche on Nyack Mountain. This slide occurred during an intense wind storm on March 2.

    Photo: md

Avalanche Discussion

This morning, an arctic air mass has settled into the Flathead, with mountain temperatures hovering on either side of zero Fahrenheit. Fortunately, the cold north and east winds have moderated from yesterday's readings which included 19 hours of strong sustained with gale-force gusts up to 73 mph at Aeneas Ridge station. Up to 12 inches of loose, dry snow remain available for transport in many north through east locations. Winds from the northeast affect vast areas, such as the front side of WMR and the Swan front, while leaving many narrow drainages in the Middle Fork corridor and elsewhere virtually unscathed. They often intensely affect the valley floor as the cold, dense air sinks and spills out to the west. 

Yesterday, observers found excellent riding conditions on north aspects from ridgeline elevations down to the valley floor. Several parties identified blower pow in areas sheltered from the wind. Saturday's sunshine left a thin surface crust on solar aspects up to 7000 feet in the Flathead. The FAC secret agent observer in the Swan noted substantial blowing snow from east to west along the Swan Crest throughout the day.

Our friends at the Gallatin National Forest Avalanche Center have a Persistent Slab problem. Over the last week, at least five human-triggered avalanches were near Cooke City. Three of these slides resulted in partial burials, and a skier-triggered slide near Daisy Pass buried the group's parked snowmobile. Get more details here. Yesterday, a skier was caught, carried, and buried up to his neck in the nearby Absarorka Range. This individual suffered a broken femur. The photo is here, and the details are here.

Sunday, we dropped the Persistent Slab problem from the Swan Range, where we have not observed slides on the buried mid-January weak layers for the past 12 days. In most locations, the weak layer is buried well over 3 feet. This is at a depth where a rider's or their machine's weight is less likely to affect. Also, a strengthening process occurs as the overlying weight compresses this weak layer. This problem remains in the Flathead Range, where the likelihood of triggering remains POSSIBLE, and in the Whitefish Range, where the possibility is UNLIKELY.

Avalanche Encyclopedia: The National Avalanche Center has issued a new and updated encyclopedia containing 257 avalanche-related terms, a new graphic design, a new hierarchical term structure and navigation, and a new user interface. The US Forest Service funded the project. The writing and content were produced by Zach Guy, former Director of the FAC. You can find it here.

State of the Snowpack and Fireside Chats. Join us at 6 pm on March 9 for a virtual evening combining two popular community ed workshops. New this season, State of the Snowpack is a presentation from FAC on recent weather and avalanches to help you digest the forecast and plan your weekend. Fireside Chats are an intimate, conversational forum for open dialogue about human and avalanche factors. With skier/psychologist Dr. Sara Boilen as our facilitator, we dig into the tough decisions, tricky snow, and lessons learned from local near misses. No registration is needed; click here for a Zoom invite.

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