Avalanche forecast

Whitefish Range

Flathead Avalanche Center
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Avalanche danger

Sun
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Out of date — this forecast expired 3 years ago.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

Recent snowfall and wind have formed drifts in unusual locations. Loose surface snow may slide easily on steep, sheltered slopes. A small slide can cause a larger, more-destructive avalanche on buried weak layers. Use short, low-consequence slopes to test the surface snow before committing to steeper terrain.

Avalanche problems

  • Persistent Slabs

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

    The weight from recent snowfall and wind-loading stresses weak layers buried 2-4 feet deep. Large, destructive avalanches ran naturally on this layer during our last loading event just over a week ago (Photo to the right/above). The added stress could also increase the chance of human-caused avalanches like the one accidentally triggered by a rider in the northern Whitefish Range on Wednesday. 

    Since mid-January, most slides on these layers occurred on mid- to upper-elevation slopes facing NW-NE-SE. However, the only way to know if a weak structure is present is to dig into the snowpack and identify it. You can use terrain choice to mitigate this problem by steering clear of the areas that are most susceptible to triggering. These include convex or rolling terrain features and rocky slopes where the snowpack is thinner. Your easiest option for avoiding this hazard is to choose lower-angle slopes away from overhead hazards.

    (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

  • Wind Slabs

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

    Yesterday (Friday), new snow and shifting winds formed slabs of wind-drifted snow on various aspects. WMR snow safety reported slabs 8-12 inches thick that ran full path. My partner and I saw less action in the Swan Lake area, where thin, isolated pockets of wind-drifted snow cracked but were reluctant to slide. Slabs will be thickest and most sensitive at upper elevations or in places favored by the recent snowfall, like Tunnel Ridge in the Flathead Range. Look for wind-drifted snow along ridgelines and mid-slope terrain features like ribs and gullies.

    Use small, inconsequential terrain features to assess this hazard. You'll know you've found a wind slab if the soft, light snow you're moving through suddenly feels heavier or becomes stiff enough that it supports your weight. Cracks shooting out from your skis or sled and collapsing the snowpack indicate the slab's instability. Slabs formed above weak, faceted snow can break above you and wider than expected. Choose terrain sheltered from the winds for a safer, more enjoyable experience.

    Additional Discussion: Loose-dry snow may sluff and run long distances in steep terrain sheltered from the wind. These may travel further than expected where the new snow rests on a crust. These slides can be dangerous if they knock you off your feet, over a cliff, or into a spot where debris can pile up deep–like a creek bed or gully. Where new snow fell on surface hoar, it may be possible to trigger small slabs of storm snow. These could be problematic when you find 8 or more inches of new snow.

    (3/6/2023)

    very small drifts produced isolated cracking.

    Photo: sw

Avalanche Discussion

Variability is the name of the game following yesterday's (Friday's) snow and wind. Weather stations across the advisory area indicated shifting winds and snowfall ranging from 1" at Stahl Peak in the northern Whitefish Range to 8" at Tunnel Ridge in the Flathead Range. The Swan Range saw 4" at Noisy Basin, with greater amounts reported south of the advisory area. New and wind-drifted snow fell on various surfaces ranging from sun crusts to facets and surface hoar. We received just a pair of observations yesterday to field verify data from the weather stations. 

Just over a week ago, a pulse of precipitation and intense winds produced large and destructive avalanches on buried weak layers in the Flathead Range and the central Whitefish Range. While yesterday's loading was generally less than that event, it's possible that favored locations have been stressed to the breaking point and buried weak layers may be more easily triggered by a rider or small surface avalanche. The latest report of a human-triggered avalanche failing on a weak layer occurred only three days ago (Wednesday) in the northern Whitefish Range.

Fireside/Snowpack Wednesday, March 15. Join us for a virtual evening combining two favorite community ed workshops. FAC Forecaster Cam Johnson will kick things off with a State of the Snowpack presentation to help you digest the current conditions and plan your next trip. Then we'll shift to Fireside Chats for open dialogue about human and avalanche factors. A recreationist, forecaster, and avalanche educator all experienced a near miss in the first three weeks of February. Together, Kat, Cam, and Meg will explore the tough decisions, tricky snow, and lessons learned from their experiences. No registration is needed; click here for Zoom. The event will begin at 6 p.m. 

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