Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Look for clues of wind-drifted snow along ridge crests. Dune-shaped drifts and cracking in the new snow are signs you have found a wind slab and should seek out terrain sheltered from the wind. It is unlikely, but not impossible, to trigger a slab failing 2 to 4 feet thick. Hedge your bets by choosing terrain with smooth, clean runouts, and avoid riding over steep breakovers. 

The avalanche danger may rise to CONSIDERABLE tonight. New snow and wind could create dangerous avalanche conditions. Avoid traveling on or beneath steep slopes. 

Problemi valanghivi

  • Wind Slabs

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

    The Aeneas Ridge weather station held sustained speeds capable of transporting snow for most of Thursday. Winds will vary from east to west in the next 24 hours. Wind speeds will also gain momentum throughout the day. 

    Be wary of slopes downwind of ridge crests and prominent peaks. Locations that come to mind are the slopes down to Picnic Lakes from Mount Aeneas, the alpine terrain along the Flathead Crest, or the higher peaks in the northern Whitefish Range. 

    Be on the watch for active wind-loading in unusual locations. If you plan to climb to upper-elevation ridgelines, expect to find existing slabs of wind-drifted snow. These will exist below ridgetops and saddles; however, their distribution may grow throughout the day due to varying wind direction and speeds. 

    (12/27/2024)

    An excellent example of cross-loaded slopes on the east face of Flattop Mountain. The wind moves from right to left in this image.

    Photo: Mark Dundas

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    Several layers of facets, faceted crusts, or surface hoar are found in the top several feet of the snowpack. The likelihood of triggering a slab avalanche on one of these weak layers is unlikely, but not impossible. The recent storm snow has added stress to these layers but is also strengthening them from the overlying weight. Warm temperatures before Christmas were helpful in the strengthening process. In some locations, they are buried to a depth that a rider or snowmachine may not impact.

    The most likely spot you could trigger a slide would be where the weak layer is closer to the surface, such as wind-scoured locations, convex rollovers, slopes peppered with rocks, or a thin area on the edge of a slab. 

    (12/30/2024)

    A rider triggered avalanche that failed on facets buried in mid-December.

    Photo: Cam Johnson

Avalanche Discussion

There is a fair amount of uncertainty in today’s avalanche forecast. Today's avalanche danger depends on the amount of new snow, the timing of new snow, and wind speeds.

The current weather pattern can deposit a substantial amount of new snow in a short time period. This one does look favorable. Precipitation is forecasted to start this afternoon, with the bulk of the moisture happening overnight. Once precipitation starts, and if snowfall rates exceed 1 inch an hour, the avalanche danger will rapidly rise. The weather forecast suggests this to occur overnight. However, if the storm arrives early and you begin to see snowfall rates exceed 1 inch an hour for multiple hours in a row, expect rising danger and adjust your terrain accordingly.

Wind direction will be relatively chaotic throughout the day and night. Winds will start out of the east and transition to the west. Wind direction and speed will also vary depending on elevation. Winds are forecast to approach speeds capable of transporting snow and have already been at those thresholds along ridge crests. One thing is for sure: we have A LOT of low-density snow available for transport.

The most notable reported avalanche from the past few days is the avalanche observed east of Peters Ridge in the Swan Range. This avalanche propagated approximately 1500 feet wide and was 2 to 4 feet thick. We suspect this may have failed on weak snow from early or mid-December. Observations from the Flathead Range generally describe a strong snowpack with few signs of unstable snow. Observations from the Whitefish Range have been sparse since the rash of rider-triggered avalanches on the 28th and 29th.

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