Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto last year. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Today’s warming could trigger wet snow avalanches in steep terrain receiving direct sun. Monitor surface conditions, as even shaded slopes may become wet enough to slide. You can still trigger a large avalanche on slopes without a supportable crust. 

 

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Recent loose wet activity has been small in size and confined to steep and rocky southerly slopes. Today's warmer temperatures could cause more widespread natural activity. Surface crusts and increasing winds might slow the onset and size of sluffs on windward and solar aspects, though slides can travel surprisingly far on a strong underlying crust. Avalanches could become possible on shaded slopes late in the day. These should be limited to the top 6 to 10 inches of the snowpack.  

    Watch for signs of wet snow, like fresh roller ball and pinwheels. Plan your day to stay ahead of the sun, including your afternoon exit. Move off of and out from under steep slopes if you start sinking into a mushy, wet snow surface.  

    (3/7/2025)

    Recent loose wet activity has been confied to steep and rocky southerly slopes.  Expect activity to become more widespread today. 

    Photo: Rob Millspaugh

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–2.5

    Slopes facing NW-N-NE-E harbor cold, dry snow with weak layers buried 2 to 3 feet deep. You can trigger a large avalanche on steep slopes where these layers are not capped by a stout melt-freeze crust.  Although less likely, you could trigger slides on solar aspects if the crust softens this afternoon.

    Weak layers may not give noticeable signs of instability like cracking and collapsing before avalanching. Slabs could break well above you, wider than expected or wrap around terrain features. Likely trigger points include convex roll-overs, slopes peppered with rocks, or wind-affected areas with variable snow depth. Small surface slides and falling cornice can trigger avalanches on buried weak layers. 

    Dig into the snow to look for (and test) weak layers before committing to steep slopes. When in doubt, opt for simple, low-angle terrain.

    (2/24/2025)

    This image shows the fracture line of a large hard slab avalanche on the east face of Mt Penrose.  Shaded slopes have breen protected from recent warming and weak layers remain intact.  Likely trigger points include convex roll-overs and slopes peppered with rocks. 

    Photo: Mark Dundas

Avalanche Discussion

Another weekend, another warm-up. This thaw won’t be a carbon copy of last weekend though. Here are some notable differences:

Last weekend:

  • Our first substantial thaw of the year. We started with dry snow on all aspects.
  • Southwest winds tapered off on Saturday and allowed further warming on slopes facing south and west.
  • Some alpine sites remained as warm as 40*F Saturday night.
  • We saw a dramatic uptick in the size and distribution of loose wet avalanches Saturday afternoon into Sunday with slides gouging to the ground and running to valley bottom.   
  • Shaded slopes were generally unaffected.

This weekend:

  • Thanks to previous thawing we have a stout crust near the surface on solar aspects. Today’s warming may destabilize recent snowfall above this crust but will struggle to penetrate further into the snowpack on these slopes.
  • Southwest winds will increase through Sunday, cooling slopes that face south and west.
  • We expect more cloud cover this weekend. However, the resulting effects on avalanche conditions are harder to predict (Read on).

All things considered, I would expect to see less avalanche activity this weekend. The greatest uncertainty is the potential for warming on shaded slopes. Cloud cover could be a major factor here. Thin layers of stratus can cause a “greenhouse effect”, but this scenario seems unlikely due to mixing and cooling from forecasted winds. If you notice the snow surface becoming wet on shaded slopes, consider taking a big step back towards low-angle terrain.

Several glide avalanches occured during last weekend's warm-up.  As temperatures warm once again, it is possible we will see more glide cracks release. "Brown Frowns" have been reported on all aspects at mid and upper elevations but are mostly concentrated on slopes that face the sun. Our friend Chris has been diligently monitoring the Swan Front, where as of yesterday (3/7) his Glide Crack Inventory reached 38! Don't dilly-dally on or below slopes where these hazards are present. 

Large cornice loom over many alpine slopes. Warming temperatures and sunshine could cause these behemouths to weaken or fall.  While large tumbling chunks of snow present their own hazards, they can also trigger large avalanches on buried weak layers.  Limit your time spent below these features especially during the heat of the day. When traversing ridgelines, stay well back from the edge as cornice can break much further back than expected. 

We are saddened to report that the recent heli-skiing incident in Alaska took the life of a member of the Flathead backcountry community. Charlie Eppard was a loving father, devoted husband, and long-time supporter of FAC and FOFAC. You can support his wife, Brittany, and their young daughter at this Go Fund Me account. An article in the Daily Interlake detailing this tragedy can be found here. 

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