Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Winds from the east will transport snow onto westerly aspects today, thickening slabs that sit above reactive weak layers buried 1 to 4 feet deep. These weak layers of surface hoar and facets are the culprits in numerous remotely triggered and accidentally triggered avalanches in the past 2 weeks. Added weight from wind loading is likely to reactivate them. Look for obvious clues like drifting snow and stick to slopes sheltered from the wind that are less than 35 degrees steepness.

Avalanche problems

  • Wind Slabs

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

    Sustained moderate wind speeds out of the east will drift snow near ridgelines (see photo) and cross-load terrain features mid-slope. Be leery of terrain where winds can channel through canyons, gain speed, and drift snow onto otherwise sheltered slopes. Signs of drifting snow and pillowy surfaces are your cues to seek wind-sheltered terrain. These slabs will be especially dangerous and more destructive where they step down to a larger persistent slab avalanche or drag you into a terrain trap.

    (2/12/2021) The plume of drifted snow off Mt. Vaught's summit shows how strong easterly winds are transporting snow at upper elevations.

  • Persistent Slabs

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

    It remains possible to trigger avalanches breaking up to 4 feet deep and surprisingly wide. The snow that rests above weak layers buried in late January is settling into a firmer slab, making triggered slides more dangerous because they'll involve more debris. Avoid steep convex slopes where you are more likely to add stress and collapse buried weak layers. Select planar slopes and avoid runouts and steep start zones above roughly 5000 feet. If your travel plans get diverted and you find yourself having to cross avalanche terrain, keep a spotter in a safe location and travel one at a time.

    (2/12/2021) This slide likely ran Wednesday. 2/10, after easterly winds transported snow over the ridge on the right onto the convexity. This winter, people have reported an unusual number of glide cracks like the one to looker's left. Some have already released.

Avalanche Discussion

February 6th was the last day of any noteworthy snow accumulation. Since then temperatures have plummeted, and winds have become more variable. Most ranges have seen a few bouts of northerly and easterly winds. These winds are drifting snow and thickening slabs on top of weak layers buried in late January. Cold temperatures and loading from wind-drifted snow are slowing the stabilization of this structure.

Observations have dropped off significantly this week due to extremely cold temperatures. We don't have detailed information from a wide area of the forecast region. Thus, the forecast today comes with a higher-than-usual degree of uncertainty regarding the sensitivity of buried surface hoar.

We do have enough clues to tell us that we are not out of the woods yet, and that it's important to stick to conservative terrain. Recent natural avalanches were likely spurred on by wind loading in Glacier National Park, shown here and here. The best clue to timing for these recent avalanches was on Wednesday when we received a bump in wind speeds out of the east, which we will see again today. Both of these avalanches failed on west-facing slopes at upper elevations. Other noteworthy observations came from Avalanche Canada in Fernie who has a very similar snowpack structure to that in the Whitefish Range. On Thursday and Friday, riders there reported human-triggered avalanches with some being triggered remotely from 50 meters (~160 feet) away.

Today winds will drift snow into fresh slabs that overlay an older generation of wind slabs as well as buried surface hoar. They will load slopes that are usually windward and safer (west, southwest, south). Sounds complex right? It will be best if you put your head on a swivel and be particularly cognizant of wind drifted snow. Expect to find slabs of drifted snow in odd places. Find safer and better riding conditions on slopes that are sheltered from the wind while keeping slope angles low, as this rider did yesterday.

The best way to appropriately manage the hazard above roughly 5000’ is by managing your slope angle. Sticking to planar slopes less than 35 degrees is your best bet. Avoid steep breakovers and don’t use treed slopes as an excuse to ride in steep terrain. Many recent avalanches have propagated and ran far and wide through vegetated slopes.

A brief summary of snowpack and avalanche conditions for the January 12 - February 12 period can be found here.

Regions covered