Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 4 years ago.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

Highlights

The avalanche danger will rise today as new snow accumulates on a  weak snowpack. If snow accumulations approach or exceed forecast totals (see weather tab), dangerous conditions will develop by this afternoon. Stick to low-angled, wind-sheltered slopes, where riding conditions are great. Avoid parking your group below steep start zones, because remotely-triggered avalanches remain possible.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3

    The likelihood of triggering slabs that break on old weak snow near the ground will increase as new snow accumulates today. New snow will thicken slabs and increase the load on a persistent weak layer that's been insistently annoucing itself since it was buried just before Thanksgiving. Heed its shouted warnings - whumpfing collapses and shooting cracks - by avoiding riding on or below slopes steeper than 35 degrees. 30 degrees, if you want to allow yourself a wider margin of safety. Beware of steep, convex spots on otherwise low-angle slopes. 

    (12/4/2022)

    Soft slabs failing on persistent weak layers at upper elevation in the Flathead Range. 

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2.5

    Light to moderate southwesterly winds have been moving snow around at upper elevations, drifting snow into slabs on leeward slopes near ridgelines and downwind of saddles that funnel winds. These slabs pose a hazard in their own right. They also compound the danger of the Persistent Slab problem, because they increase the load on buried weak layers. Thus, it's best to keep your distance from slabs of drifted snow today. Stick to slopes sheltered from southwesterly winds or less than 35 degrees steepness. Cracks in dense, hard snow are a clear announcement of this hazard. It is more widespread as you climb higher in elevation. 

    (12/4/2022)

    Scouring, wind-hardened surface, and thin, hard slabs near ridgelines. Swan Range.

    Photo: FAC

Avalanche Discussion

Keep these big picture thoughts forefront in your mind today:

  • Accumulating snow will increase the likelihood of triggering slabs that break 1 to 3 feet deep on old 
  • Accumulating snow will increase the potential size of triggered or natural slides
  • Accumulating snow will increase the variability of conditions from slope to slope.

As likelihood, consequences, and uncertainty rise, I fall back on something measurable and knowable - slope angle. That's easy when soft, low-density surface snow makes for great riding in most terrain, which are the conditions present across most of the forecast region now. Additionally, on lower-angled slopes you're less likely to hit shallowly buried rocks and stumps, because you or your machine don't sink as far below the snow surface turning or climbing.

Today, the upper limit of "lower-angled" is somewhere between 30 and 35 degrees, depending on the slope configuration and your risk tolerance. Stick closer to 30 degrees for slopes above terrain traps or terrain where more than about 8 inches of new snow has accumulated since Monday morning. Use an inclinometer - your phone likely has one - to measure slope steepness. Consider whumpfing collapses are the snowpack's equivalents of a dog growling or raising its lip to warn you that a bite is coming if you venture closer. 

The Whitefish Range is forecast to miss out on most of today's snowfall, but one recent report suggests that the Persistent Slab structure there may be more reactive. 

Complicating the danger today is a growing hazard of wind slab avalanches. Reports from Monday described moderate wind loading in the Apgar and Swan Ranges. Wind speeds are forecast to rise today, so expect the distribution and thickness of wind slabs to increase today. As you approach ridges or other terrain exposed to the wind, steer clear of steep slopes with fresh deposits of wind-blown snow. These will feel firmer and denser than snow on sheltered slopes. 

Education - Our next Avalanche Awareness presentation is this  Wednesday, December 7, at Whistling Andy Distillery, Bigfork. You can get more details about this free event here. Next week, we will offer an Avalanche Awareness presentation Wednesday, December 14, at Penco Power Products, Kalispell. You can get more details about this free event here.

Observations - Thanks to everone 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 vague or specific 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. 

Preseason restrictions on uphill travel are in effect at Whitefish Mountain Resort.

Regions covered