Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

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

At mid and upper elevations, it's possible to trigger slabs of drifted snow a foot or more thick. In wind-sheltered terrain, sluffs of loose dry snow can pose a hazard in very steep, confined terrain or above terrain traps. Test slopes and the texture of the near-surface snow can give you reliable data about these hazards. Hard over soft? That's Wind Slab conditions. Loose and cohesionless over hard? That a Loose Dry hazard. This is our last daily forecast for the 2020-21 winter. We'll issue conditions updates twice a week through the end of April. 

Avalanche problems

  • Wind Slabs

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

    As you move higher in elevation today, your chances of encountering recently-formed slabs of drifted snow increase. These slabs come in two flavors: thin, soft drifts that don't propagate widely, and unpredictable hard slabs a foot or more thick. The first may camoflauge the second. They'll be most widespread near ridges and summits, in terrain with large fetches and narrow catches. Picture a broad windward ridge that funnels snow into the top of a narrow chute. You may also find isolated slabs well below ridges, in drainages that funnel westerly winds. Probing and digging are your best tools for identifying these conditions in this terrain. If you can punch through a harder layer into soft snow, consider slope angle and consequences above and below you. 

    (4/9/2021) Small wind slab triggered on a test slope. Utilizing small, inconsequential terrain features, like this one, is a good tool to test how reactive slabs are.

  • Loose Dry

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

    Shaded and wind-sheltered slopes hold cohesionless dry snow. This snow can sluff on very steep slopes - 40 degrees or more. These sluffs can be dangerous where there's more than 8 inches of loose snow above firm crusts or hard, old snow.  And where they can sweep you into or over a terrain trap, such as cliffs, tree wells or gullies. Pick lines that allow you and moving debris to part ways amicably.  

    (3/23/2021) Loose, dry avalanches on steep north-facing slopes in the Middle Fork of the Flathead Range. These were easy to initiate with ski turns and large enough to push us around. We avoided getting tangled up in these by managing our sluffs.

Avalanche Discussion

Strong winds and snow showers have left scattered avalanche hazards across the forecast region. The primary concern is slabs of drifted snow left by an extended period of strong westerly winds. Since Wendnesday, ridgeline stations have recorded several bouts of winds averaging near 20 mph, with gusts of 40 to 70 mph. The Swan and Flathead crests saw the strongest winds, and observers reported plumes of blowing snow off the high peaks in the Flathead Range on Friday.

The winds haven't had much snow to move around, and much of what was available was graupel. At mid elevations in the Swan Range Saturday, I found thin soft drifts near ridges, and in a few spots, older hard slab less than a foot thick. Similar conditions exist throughout the region. The thickest, most dangerous slabs are in at upper elevations, in areas where more than a few inches of new snow accompanied the winds. That's primarily the Swan crest, and the high peaks of the Flathead Range, Lake McDonald valley, and Stevens Canyon. Similar slabs are isolated at mid-elevations. Wind speeds dropped overnight and are forecast to remain light until later this afternoon. With little additional drifting, I expect existing slabs to stabilize.

A second concern that's less widespread across the region are Loose Dry snow avalanches. These can pose a hazard where more than about 8 inches of loose snow sits on firm old snow or melt-freeze crusts. Those conditions are isolated in the Whitefish and Swan Ranges, where recent snow accumulations are generally less than 8 inches except at high elevations. In the Flathead Range on Friday, Clancy found he was able to trigger small sluffs of dry snow on very steep, northerly slopes at mid-elevations. With another 3 to 5 inches of snow Saturday, this hazard will be more widespread in that zone today, with sluffs possible in very steep, wind-sheltered terrain at mid and upper elevations. The debris from these sluffs can be surprisingly dense, so pick terrain that isn't confined or over terrain traps. 

Most windward and sunny slopes have a stout melt-freeze crust that's unlikely to break down today. 

Pro tip: Check back for conditions updates through the end of April. We'll be issuing these twice a week, unless conditions change dramatically enough to warrant more. Your observations can make those more accurate, so let us know what you find on your late season adventures. Your friends in the backcountry community will appreciate those updates too. 

A huge thank your to everyone who's contributed to our forecasts this winter: volunteer field partners, interns Zach, Jeremy, and Sarah, observers, our partners at Whitefish Mountain ski patrol, the Patrol Fund, and the Burlington Northern avalanche program, anyone who shared near miss and accident information or observations, and the Friends of the Flathead Avalanche Center! 

Regions covered