Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

The avalanche hazard will increase today as air temperatures warm into the 40s at mid elevations and clouds diminish this afternoon. Plan routes that keep you out from under steep slopes and corniced ridgelines. The most hazardous terrain will likely be steep, upper elevations slopes where the snow is turning wet for the first time.

Lawinenprobleme

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Natural and triggered wet snow avalanches are likely on slopes steeper than about 38 degrees. At low and mid elevations, wet snow avalanches will consist of coarse-grained older snow that hasn't refrozen. Triggered or natural slides at these elevations may gouge into older snow, entraining dense debris that's hard to escape. Avoid riding under gullies and below rocks, especially during periods of sustained sun. At upper elevations, these slides will involve cold snow that's getting wet for the first time. Clear signs of these conditions are rollerballs releasing naturally or from your board(s) or machine. 

    (3/18/2022)

    Wet Loose debris came within 50 feet of reaching the Marion Lake trail. This path slides occasionally and is located near the wilderness boundary sign.

    Photo: Paul Fotter

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Slabs perched on weak faceted snow from early March may be more sensitive to triggering today. You can reduce the uncertainty about this problem by sticking to slopes less than about 35 degrees that have a planar or concave profile. Pick ascent routes and regroup spots that aren't below steep start zones likely to harbor this structure. Treat whumpfs or collapsing sounds as sirens warning that slopes are unstable.

    (3/17/2022)

    The kind of terrain where the Persistent Slab hazard is likely to linger. This avalanche occurred on a southeast aspect above 6000 feet.

    Photo: Pete Costain

  • Cornices

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Keep an eye above you, and don't linger under looming cornices. These are weakening and sagging in the warm temperatures. They can break and trundle large amounts of very hard debris down slopes below them. Stick to the windward sides of ridges, well away from cornices, which can break surprisingly far back.

    (2/11/2022)

    Large seasonal cornices from southwest winds cap a ridgeline. Warm sunny weather can weaken these features resulting in cornice fall with the potential to trigger an avalanche on the slope below.

    Photo: Pete Costain

Avalanche Discussion

The freezing level is between 6000 and 6500 feet this morning, and overnight clouds prevented wet snow surfaces from refreezing. You won't have much, if any, window for traveling without considering wet snow avalanche hazards today. Those will come in two flavors. At low and mid elevations, it's near-surface snow that's been through a cycle or two - or ten - of melting and freezing. Water in this coarse-grained snow leaves it cohesionless and easily susceptible to getting knocked downslope. Triggers can be you, or snow falling onto it from trees or rocks,. It usually takes a very steep slope for these to move far - 38 degrees or so - but once moving, they can entrain dump-truck loads of very dense debris that's hard to esape. If you're sinking in past your boot tops, you've found these conditions. The second flavor is cold, dry snow that's getting moist for the first time. Those conditions are most likely on northerly slopes at upper elevations. 

There's a good chance the warm temperatures are de-stabilizing the near-surface Persistent Slab problem found on northwest through northeast to southeast aspects. This structure has been trending to unreactive over the past week. However, rapid settlement and consolidation of the slab may be adding some hiccups to that trend.  I noticed the crown and debris of a relatively-recent, large, natural avalanche on a mid-elevation, southeasterly slope in Skiumah Creek Tuesday, though I didn't see fracture lines on similar slopes in Cascadilla Creek. I'd dig before committing to large terrain that's likely to harbor this structure, particularly around 6000 feet. That's where most of the reported activity occurred 10 days ago, and above this morning's freezing line. For a more in-depth discussion of the development of this hazard, see Mark and Megan's conditions blog from Friday, March 18.

Lastly, large cornices loom above many leeward slopes. They're sagging in the warm temperatures, incresing the potential for chunks to break off and trundle downslope. These can pose a hazard in themselves; if you were below, it'd be like having refrigerators rolled at you. Or they can trigger slides on older weak layers. Best to avoid being under steep slopes capped by cantilevered snow.

A cold front late tonight may bring freezing temperatures  back to mid elevations by tomorrow morning.

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