Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
1 · Low
Treeline
1 · Low
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Out of date — this forecast expired 4 years ago.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

It's unlikely but not impossible to trigger a slab failing 1 to 3 feet thick on shaded aspects. Safer conditions exist on slopes that face south and west. Duck in and steer around small and isolated slabs of drifted snow as you climb in elevation. These will likely only be hazardous in areas where being caught in a small slide would take you over cliff bands or through densely treed slopes. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    Persistent weak layers buried roughly 1 to 3 feet below the snow surfaces have snow no recent signs of instability. Snowpack tests and recent observations confirm that the snowpack is strengthening. Persistent weak layers are unpredictable, so be aware of this problem despite today’s decreasing danger level. Low danger does not mean no danger, and it is still a good idea to mitigate the risk with terrain choices and travel decisions. Steer around convexities and choose routes free of terrain traps.

    (3/17/2022)

    The crown of a soft slab avalanche is partially filled in from new and blowing snow. This avalanche is on a southeast aspect above 6000 feet.

    Photo: Pete Costain

Avalanche Discussion

The weather forecast for today doesn't show any significant change that will alter the avalanche forecast. Today's danger is predominately looking at recent trends and past weather events. Let's start with the current state and trend of buried persistent weak layers from early March? 

Most recent Red Flags:

  • The last collapse was in southern Glacier National Park on March 17th (4 days ago) and occurred in the middle elevation band on an east and north aspect. 
  • The last reported avalanche was also in southern Glacier National Park and was estimated to have failed March 16th (5 days ago). This Large (D2) slide occurred at about 7200 feet on an east aspect. 
  • The peak of natural and human-triggered activity occurred on March 12th and 15th. Nearly all slides were triggered between 6000 and 6500 feet and on north to east aspects.

With a decreasing trend in reported activity, Megan (March Intern) and I set out on Sunday to dig and test weak layers near sites where Mark found unstable results on the 14th. Megan and I were pleased to find mostly stable results. We had only one test propagate, and this was with hard force. Other observations from the past few days show similar results and confirm weak layers are gaining strength.

There is a higher degree of uncertainty in the Swan Range due to a lack of observations. We anticipate the weak layer is distributed and behaving similarly across the forecast region. 

The evidence shows it is unlikely to trigger a slab 1 to 3 feet thick. The caveat is it still exists, and the consequences could be large if triggered. Buried near-surface facets that were once reactive require patience and diligent travel technique. If conditions and your decisions point you towards northerly and easterly facing aspects, stack the deck in your favor by selecting planar slopes with clean runouts - essential travel advice if you are stepping out into steeper terrain! Avoid convex rollovers and choose slopes that terminate in fanned runouts free of trees and rocks. Keep your eyes on your partner from a safe location. If you have some uncertainty, dial back your slope angle to 30 degrees or less or switch aspects to those facing south and west. South and west aspects have a few crusts above the weak layer, making it even more unlikely to trigger.

Winds drifted new snow into small, reactive slabs on Sunday. I anticipate slabs to be stubborn to trigger today and only a hazard in consequential terrain. Keep an eye out for pillowy-looking surfaces and corniced features. Tuck in below and steer around wind drifted features searching for cold, dry snow.

Expect a warming trend for the remainder of the workweek. 

Regions covered