Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous conditions exist at upper elevations in the aftermath of Thursday's unexpectedly wet storm. You can trigger slabs of new and drifted snow that can break 1 to 2 feet deep. Fresh avalanches, shooting cracks, and snow that feels or sounds hollow are clear signs of unstable snow. Slopes less than 35 degrees offer great riding with lower risk.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    Avoid slopes steeper than about 35 degrees with dense slabs of new or drifted snow a foot or more thick. Newly-formed slabs will be more reactive to your weight or the weight of your snowmachine on steeper slopes and where they've been stiffened or thickened by recent winds. Sheltered areas at mid elevations may harbor snow that feels upside-down - denser at the surface than below - that may also be reactive. Mid-slope convexities are likely trigger points in these conditions. Planar slopes with runouts clear of terrain traps and obstacles offer the safest riding today.  Avoid playing in the runouts of steep start zones where you see blowing snow above you. 

    (1/20/2022)

    A small triggered slab from Thursday afternoon. Today, slabs will remain reactive but be bigger today and more dangerous, especially at upper elevations.

    Photo: Rob Millspaugh

Avalanche Discussion

On the day my social media post joked about things not going according to plan...the forecast did not go according to plan. Or more accurately, Thursday's storm proved wetter, warmer, and less windy than forecast. Nearly all of the region saw new snow totals that met or exceeded forecast accumulations, with the rain-snow line climbing to between 4500 to 5000 feet, roughly 500 to 1000 feet higher than forecast.  Though freezing rain was a possibility Thursday, it just flat out poured late Thursday. 

The snow tapered off last night and temperatures cooled to below freezing at nearly all stations. The storm pummeled the Whitefish Range where the forecast 4 inches of new snow more than doubled to 10-12 inches and 0.7-0.85 inches of water. Storm totals were closer to the forecast in the the Swan Range, which looks to have picked up 8 to 10 inches, with 1.5 inches of SWE at Noisy Basin. Snow accumulations dropped off further east, with the Flathead Range picking up  8 to 10 inches and 0.7 to 0.9 inches of SWE. Accumulations look to be about half that along the Continental Divide. Winds were generally not as strong as forecast, though at upper elevations they were sustained enough to drift and stiffen the new snow into small slabs that a person could trigger.

Three important factors in today's forecast. First, Thursday's snow fell on weak or slick snow surfaces: low-density snow, melt-freeze crusts, and maybe some surface hoar or facets. Second, the storm ended warm, so the upper few inches of new snow are denser than the lower few. Lastly, I'm uncertain how strong winds were near the crest of the Swan Range; the Aeneas Ridge wind sensor may have rimed up early Thursday afternoon. Because it's usually our windiest station, I'm going to assume the winds kept blowing. Other stations showed moderate winds with strong gusts, with six hours of gusts over 30 at the WMR Summit station last night and gusts into the 40s at Tunnel Ridge. 

 So today's avalanche hazards involve slabs that break in or at the base of the new snow. These may run longer and faster than expected on the slick crust that was Wednesday's snow surface. The likelihood of triggering slabs and the potential size of avalanches will be greatest in areas that recieved the most snow - the Whitefish and Swan Ranges - and at upper elevations, where winds have drifted snow and stiffened slabs. You're less likely to trigger dangerous slabs at mid elevations and in areas that recieved less snow, like the Flathead Range around Essex, John F. Stevens Canyon, and areas near the Continental Divide. Below about 5000 feet, expect a melt-freeze crust at the snow surface; you're unlikely to trigger slabs where this exists.

Our Conditions Blog tab includes a great summary of the week's conditions. 

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