Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Look for changes in the snow’s surface as evidence of recent winds. Below ridgelines, tops of chutes, and cross-loaded gullies are suspect areas for wind-loading. Continue to assess the upper snowpack for new weak layers buried under building slabs.

Avalanche problems

  • Wind Slabs

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

    Recent snow and increased southwesterly winds thickened slabs on the leeward sides of ridges and cross-loaded gullies further downslope. Slabs may be larger and more dangerous in the Swan Range where more snow fell on Sunday. Fresh slabs of drifted snow rest above persistent weak layers. A snowpit test yesterday showed propagation with easy force roughly 8 inches below the surface. Freshly formed slabs on persistent weak layers may break wider than expected, be remotely triggered, or wrap around terrain features. Shooting cracks and whumpfing collapses are signs to keep an eye out for today. 

    (1/3/2023)

    Active blowing snow and drifted features, like this one, are your two primary tools for avoiding getting caught in an avalanche today. 

    Photo: Ted Steiner

Avalanche Discussion

Sunday nights storm dropped anywhere from 6 to 10 inches on the Swan and Flathead Range, and 3 to 5 inches in the Whitefish Range. We are uncertain exactly how much new snow fell in the northern Whitefish Range and near the Flathead Crest. This snow fell on weak layers of facets, faceted crusts, and surface hoar. Snowpit tests yesterday (Wednesday) showed propagation with easy force. Utilize small test slopes to test how sensitive new snow is. Look for drifting snow and dune-shaped drifts for places to avoid. 

After 40 days of listing a Persistent Slab Problem, we removed it today from our problem list. The decision was not made lightly and was made as a forecast team. As we’ve discussed in many of our previous forecasts, this is a complex problem that is challenging to predict, as well as manage. 

Our discussion started with a review of the time that has passed since we have observed or received reports of avalanches and/or instabilities associated with the mid-November buried weak layer. The last collapse reported occurred almost a week ago (January 6) at a mid-elevation slope, in the southern Whitefish Range. Roughly two weeks ago, Cam experienced a loud collapse (December 28) in the Swan Range. The last avalanches that failed on this layer were during the Christmas rain event. Since the Christmas rain event, we have received a total of 96 observations. 

Which brings us to the second consideration: the crust. The Santa Soaker, aka the atmospheric river that soaked the area and then froze to create the stout Christmas Crust complex, ultimately limits our ability to impact the buried persistent weak layer, where it exists. Given the observations that the Christmas Crust extends to upper elevations along with the time that has passed, we removed the Persistent weak layer, as a current problem. It is important to keep in mind that there is still a lingering potential to trigger this weak layer in areas with a shallow snowpack. Given the total number of observations, lack of signs of instability, and the stout Christmas Crust, we feel it is now very unlikely to trigger this weak layer.

Regions covered