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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Highlights

Pay attention to newly formed slabs of wind-drifted snow. Dunes, pillows, and cornices are features that will key you into wind-affected terrain. Shooting cracks from your machine or skis are signs of unstable snow. Although unlikely, you could trigger a large destructive avalanche on buried weak layers in steep rocky terrain.

Avalanche problems

  • Wind Slabs

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

    Today, winds will shift back to the west, with moderate gusts redistributing snow. Several days of north and east winds have built slabs reactive to riders' weight on various aspects. Expect to find fresh wind features in the usual and unusual locations. As you gain elevation, slabs may increase in thickness and become more widespread. These may form on crusts, which makes them easier to trigger and potentially propagate wider than expected.

    Fresh cornices, dunes, rippled snow surfaces, and areas with stiffer snow are telltale signs of wind transport. Cracking beneath your boards or machine indicates an unstable slab. 

  • Persistent Slabs

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

    You can reduce your risk of triggering a large avalanche by avoiding steep, rocky, heavily wind-affected terrain on shady slopes, where buried weak layers remain preserved. The recent heat wave helped strengthen buried weak layers, but triggering a 2-4 foot-thick avalanche remains possible. 

    The persistent slab is a complex problem to manage. You may not experience snowpack collapsing or other obvious signs of instability before the slope you are on avalanches. The easiest way to manage this problem is to choose lower-angle terrain without convexities. Locations harboring a supportable near-surface crust will be safer as your weight may not impact the buried weak layers. 

    (3/15/2024)

    This image is the crown of a very large hard slab that failed on a steep, unsupported southeast slope on March 15th. Triggering a hard slab avalanche is most likely in rocky, steep, complex terrain like this. 

    Photo: BNSF Avalanche Safety

Avalanche Discussion

Cool air and breezy north and east winds dropped south out of Canada on Thursday night and initially impacted the John F Stevens Canyon area. This airflow slowly migrated to other zones and eventually reached the Swan Range on Saturday afternoon. These winds transported recent snow onto atypical slopes throughout the area at all elevations.  

Yesterday, a rider in the Swan Range triggered a slab avalanche in wind-stiffened snow and, thankfully, could ride out of the slide unhurt. This occurred on a north aspect and broke approximately 100 feet wide. Accounting for localized features that shape how winds transport snow is vital for determining the varied aspects on which slabs develop. 

Shifting winds today will contribute to slab formation and will remain the primary avalanche problem. Snow untouched by north and east winds is available for transport and will likely form fresh wind slabs. Yesterday, observers in the southern Whitefish Range reported winds building small pillows, reactive slabs, and cornices in atypical locations along ridgelines. Rob and I found similar conditions in Noisy Basin, where we triggered small 6 to 10-inch wind slabs. 

It's important to note that despite the size of most of these wind-driven features, even small slides can have serious consequences. They can knock you off your feet and send you to places you don’t want to go. Managing this avalanche hazard should include paying attention to the terrain below and above you. 

Additionally, our dynamic spring weather makes forecasting especially tricky. Afternoon clouds with a shift in the winds brings the threat of increasing temperatures and a chance for wet-loose activity. If you notice rollerballs or snow transitioning to moist, it may be time to move to lower-angled slopes or more shaded aspects.

We are still listing a Persistent Slab problem due to the uncertainty of the past week's warm weather. The chance of triggering a large avalanche on a buried weak layer appears to be trending towards unlikely. We trimmed the problem to upper elevations and with more observations, we hope to remove this problem from parts of our advisory area soon.

Help avalanche researchers! The Colorado Avalanche Information Center, the Avalanche Research Program at Simon Fraser University, and the U.S. National Science Foundation National Center for Atmospheric Research are researching how skiers, snowmobilers, snowshoers, ice climbers, and anyone else who travels in the backcountry interpret avalanche forecast information. This research includes a survey to understand better how helpful avalanche forecast information is for trip planning. 

Completing this survey will take approximately 20 minutes. Thank you!

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