Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
View on map

Avalanche danger

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Out of date — this forecast expired 5 years ago.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

Highlights

You can trigger slides large enough to bury or injure you on steep slopes that harbor freshly-deposited slabs of drifted snow or recently buried weak layers. Both of these hazards are more widespread at upper elevations, and more likely on slopes steeper than about 35 degrees. Wind-sheltered slopes less steep than 35 degrees offer great riding with less danger.

Avalanche problems

  • Wind Slabs

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

    You can trigger freshly-deposited slabs of wind-drifted snow on steep slopes that have been top-loaded or cross-loaded by southwesterly winds. These slabs will likely be soft, a foot or so thick, and confined to terrain that efficiently collects wind-blown snow, like the tops of chutes, lee slopes below ridge crests, and the lee sides of gullies. Older slabs of drifted snow may still be sensitive to the weight of a rider or machine on isolated south, southwest, and west aspects at mid and upper elevations. Stay alert for snow that feels dense, hard, or hollow; use hand pits or probe to check the thickness of these deposits.  If you find drifted snow more than about 8 inches thick, avoid slopes steeper than about 35 degrees. Shooting cracks are a clear sign of this hazard.

    (2/2/2022)

    The zigzagging crown of a large avalanche that ran on a southwest facing slope, cross-loaded by wind in southern Glacier Park on the night of 2/1-2/2

    Photo: Adam Clark

  • Persistent Slabs

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

    Think twice before riding shaded and wind-sheltered slopes steeper than about 35 degrees, or lower-angled slopes with steeper, convex rollovers. These are the slopes where you can trigger large avalanches that break 10-18 inches deep on weak layers buried by recent storm snow and drifted snow. These weak layers often show in snow profiles as distinct grey lines. Snowpack test can be unreliable indicators of stability, and you can trigger slides from adjacent slopes or below. The most straighforward way to manage this unpredictable hazard is to avoid terrain likely to harbor the weak layers.

    (2/2/2022)

    Surface hoar was well preserved in snow pits on the east side of the Swan Range, though it did not fail in stability tests

    Photo: Guy Zoellner

Avalanche Discussion

The damage could have been worse. The blast of northerly and easterly winds Tuesday don't seem to have widespread effects on the snow surface at mid elevations. Riders reported soft snow on sheltered southerly slopes near Essex and on the South Fork side of the Swan Range. East of Whitefish Mountain Resort, a rider reported scattered drifts on northerly and easterly slopes. Where those observers did find wind-blown snow, the slabs were sensitive to a person's weight but only a few inches thick. We've had one report of a large natural avalanche on a southwesterly slope. These older slabs may remain sensitive to a rider with today's warming temperatures. They may also exist in atypical locations, like gully walls and cutbanks near valley bottoms.

Equally important - and complicating the hazard - are freshly-deposited slabs of drifted snow. Winds returned to their more typical southwesterly direction late Wednesday, and have gusting near transport thresholds at many stations, with the highest, most exposed stations (Aeneas Ridge, Sperry) showing hourly averages over 20 mph since late Wednesday. With plenty of soft snow available to blow around, I expect some newly-formed wind slabs to pose a hazard at upper elevations. 

It remains possible to trigger slides that break in older snow buried early this week. On north through east aspects above about 6000 feet, many slopes harbor layers of surface hoar and facets buried 10 to 18 inches below the surface. A rider triggered a slide that broke on the buried surface hoar on Tuesday, east of Whitefish Mountain Resort. Other riders reported audible collapses near Essex Monday and Tuesday. Guy and Erich found the surface hoar in Doris Creek, on the east side of the Swan Range, Wednesday. So far, the buried facets around the mid-January crust have been unreactive. As the slabs above these collapsible layers consolidate, they may become more easily triggered. You can identify these layers relatively easily in snow profiles, and column tests can indicate whether they can propagate. A lack of propagation doesn't guarantee stability, so it's best to simply avoid likely trigger points on slopes that harbor this structure.

Last night, we received images of a very large natural avalanche on the east face of Mt. Grant. The avalanche likely released last week, perhaps Saturday. It's a clear example of the Deep Persistent Slab avalanche hazard above 8000 feet that we described last week. That problem appears dormant for now. Notably, this slide and the slides in Skiumah Creek earlier in January released on steep, exposed bedrock. I'll be checking my mapping program for similar slopes overhead when I head into upper elevation terrain for the rest of the season.

Regions covered