Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Clearing skies and warm temperatures will cause increasing danger today. Move to less steep or more shaded terrain during the heat of the day or if you see rollerballs tumbling downhill. Limit your risk by choosing slopes where a slide will not carry you over a cliff, through trees, or into a gully. Triggering a large avalanche on northerly alpine slopes is unlikely but would have severe consequences.

Avalanche problems

  • Loose Wet

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

    Recent observations have noted moist surface snow on most aspects and elevations. Riders have also reported triggering rollerballs and small sluffs. Today will be sunnier and warmer than the past few days. The strong spring sun can destabilize the surface snow surprisingly fast. Look for signs of an impending wet loose problem, like snow shedding from the trees or roller balls scuttling down steep slopes. These are signals to move to less steep and/or more shaded slopes.

    This problem will develop most quickly when dry snow transitions to wet for the first time, like areas favored by recent convective snowfall. Slopes previously warmed by the sun likely have a series of melt-freeze crusts near the surface, which can delay the onset of wet loose activity.  However, today's forecasted sunshine may be enough to nuke its way through. Plan your route so you are off of and out from under steep, sun-baked slopes during the heat of the day. 

    (3/27/2024)

    Terrain like this steep rocky slope will be the first to produce natural wet loose avalanches.

  • Persistent Slabs

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

    The chance of triggering a large avalanche on weak layers buried 2-4+ feet decreases as these layers gain strength. The most likely place to trigger one of these beasts is in steep, rocky, and/or wind-swept terrain on the north side of the compass. Here, the weak layers are closer to the surface and possibly better preserved. 

    Hard slab avalanches can fail without any prior sign of instability, break far wider than expected, and are extremely difficult to escape. If you choose to ride where this problem exists, opt for slopes with a thicker, more uniform snowpack free from convexities. Steer around areas where the snowpack is of variable depth, like slopes peppered with rocks.  Note that recent southwesterly winds have rebuilt cornices that are looming above slopes harboring buried weak layers.  Today's warmth and sunshine could be enough to calve off chunks capable of triggering an avalanche.

    (3/17/2024)

    This is a hard slab avalanche on Nyack Mountain that failed on a northeast aspect at upper elevations on March 16. This slide likely failed on a layer of facets above the early February crust.

    Photo: Mark Dundas

Avalanche Discussion

Observations from this week indicated a coy wet loose problem that arose during passing windows of sunshine. Clearer skies and warmer temperatures today will make wet loose more menacing today, but not necessarily impressive. The real action should kick off during the ridge of high pressure early next week.

With waning southwesterly winds, we’ve removed the wind slab problem from all three zones. However, I suspect a rider can still find and trigger a wind-stiffened slab in extreme terrain, particularly in areas favored by recent convective snowfall and/or wind. Some areas that come to mind are:

  1. Aeneas Ridge, which routinely sees the highest sustained winds in our forecast area;
  2. The upper McDonald Valley, where Flattop Mountain picked up 7” of snow and 0.7” SWE yesterday
  3. Near the continental divide, where one rider reported widespread wind effect, and another reported a small natural slab avalanche

We’ve dropped the Persistent Slab problem in the Swan Range. Repeated observations, like FAC's from Sixmile, documented that this area’s buried weak layer is non-reactive, and with no reported avalanches, we feel comfortable removing this problem. 

Help avalanche researchers! The Colorado Avalanche Information Center, the Avalanche Research Program at Simon Fraser University, and the U.S. National Science Foundation National Center for Atmospheric Research are researching how skiers, snowmobilers, snowshoers, ice climbers, and anyone else who travels in the backcountry interpret avalanche forecast information. Part of this research includes a specific survey to better understand how useful avalanche forecast information is for trip planning. 

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