Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Danger will increase throughout the day as heavy snow -and possibly rain- falls on weak surface snow.   Winds will form thicker slabs in gullies and along ridges. Watch for signs of instability in the new snow, like cracking around your feet or machine. Roller balls and pinwheels are signals to make an early exit. Small slides may step down to weak layers near the ground, resulting in a large avalanche.

Avalanche problems

  • Loose Wet

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

    Warm Pacific air entered our area overnight and will strengthen into tomorrow. A wintry mix of precipitation will accompany the warm atmosphere this afternoon. Freezing rain or rain may fall on very cold surface snow resulting in loose avalanche activity. This problem will develop later this afternoon and intensify overnight. Loose slides may grow impressively large due to the copious amounts of loose surface snow. Snow falling from tree branches is a sign that the snow is warming. Rollerballs or pinwheels signify that the snow surface is becoming unstable. This afternoon, limit your time spent above terrain traps and beneath steep open faces. 

  • Storm Slabs

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

    Observers noted touchy storm slabs in yesterday's cold fresh snow. This new snow fell at readings below zero but was much denser than the snow it buried. Warming temperatures overnight have increased this upside-down near-surface problem.  This afternoon, a Pacific storm will enter the area depositing heavy, dense snow, which may overload the underlying low-density surface. Triggered slides have the potential to entrain large amounts of surface snow. Look for cracking beneath you to identify a slab. Choose lower-angled slopes free of overhead hazards for a safer experience.

    (12/23/2022)

    Thin storm slabs released from the weight of a skier in today's new snow. Slabs were thin and harmless in the terrain we traveled.

    Photo: Mark Dundas

  • Persistent Slabs

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

    Large avalanches failed on weak snow near the ground during our last loading event.   New snow will once again increase the strain on buried weak layers.  Whumpfing collapses and shooting cracks are clear indications to move to slopes less than 35 degrees. For a greater margin of safety, make that less than 30 degrees. Small slides can step down and result in a more destructive avalanche. 

    (12/22/2022)

    Crowns from one very large or multiple large to very large natural avalanches at the head of Sheep Creek, south of Mt. Cameahwait. These likely involved wind drifted snow. 

    Photo: Adam Clark/ BNSF

Avalanche Discussion

I’m starting to rethink all the “warm” wishes I offered this holiday season.  The Heatmiser cometh. For the second day in a row weather stations are recording an increase of 18F during the last 24 hours.  Tonight, mountain temperatures might cross north of freezing for only the second time since Thanksgiving. Warm and wet pacific air has us in the cross hairs of its Red Ryder, carbine action, 200-shot, range model air rifle, with a compass in the stock and this thing that tells time.

We’re dealing with a lot of uncertainty this weekend.  Backcountry observations are still lacking following the cold-snap and the rain/snow line associated with Rain-on-Snow events like this are notoriously difficult to predict.  Let’s focus on what we do know:

  • The snowpack has seen a dramatic increase in temperature since Thursday morning's widespread lows of -20 to -35F.
  • Temperatures will continue to increase and the rain/snow line will likely rise in elevation.
  • New precipitation will fall on abundant low-density snow surfaces. 
  • Where this falls as snow, it will be more dense and cohesive than the underlying snow, making it likely to behave as a slab. 
  • Where it falls as rain, it may destabilize surface snow and cause wet loose slides.
  • Winds from the Southwest will drift snow onto typical lee aspects. 

Danger today might start as Moderate but will increase to Considerable once the Heatmiser arrives.  Be vigilant in case he makes an early arrival.  

If FAC is on your list for some last-minute holiday shopping, one thing we’re needing is a better tool for estimating the rain/snow line of incoming weather systems like today's. The Desert Research Institute has developed the RainOrSnow app to collect crowd-sourced data to help forecast mixed precipitation events.  Use it while you’re out in the mountains to let them know what type of precipitation you’re seeing, or as you’re laying in bed listening to rain pound on the roof.

Training: Now's a great time to hone your companion rescue skills. Transceiver parks are open at Whitefish Mountain Resort, one at the summit and one adjacent to Grey Wolf. Both are accessible to snowmachines. You can get more details about training and education opportunities events on our events calendar.

Observations - Thanks to everyone who's been utilizing our new observation submission page. Try it out and help your community by sharing what you see in the backcountry. The form requires you to fill out the location fields and put a dot on a map. Be as specific or vague as you want. Our new Observation View page highlights signs of instability and allows you to filter by date or zone to pull out reports relevant to your objectives.

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