Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Wed
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Very dangerous avalanche conditions exist due to unseasonably warm temperatures and a poor snowpack structure. Avalanches large enough to destroy a wood frame house have failed naturally over the last two days. The signs are clear: stay out of and out from underneath steep slopes.

Problemi valanghivi

  • Persistent Slabs

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

    Slab avalanches, both Persistent Slabs and Wet Slabs, are failing naturally at middle and upper elevations. All of the recent natural avalanches are large enough to bury, injure, and kill a person. Treat all steep slopes as candidates for a large and deadly avalanche. Give the runout of large avalanche paths a WIDE margin for error since avalanches may run long distances. Persistent Slab and Wet Slab avalanches are unmanageable if caught and may fail without warning.

    Crowns span all start zones visible on the mountain. These avalanches likely destroyed acres of forest. 

    Photo: Rob Millspaugh

  • Loose Wet

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

    Solar radiation and warm temperatures will continue to weaken the snow surface and cause it to slide. Plan for this problem to exist on all aspects due to unseasonably warm temperatures. Rollerballs and point releases out of steep, rocky areas are signs of an impending Wet Loose cycle. Wet loose avalanches have been reported nearly every day for the last week. 

    (1/29/2024)

    Wet debris piled up on a road cut in Canyon Creek. Similar avalanches to this one have occured in other parts of the forecast area. 

    Photo: Jessica Bonomo

Avalanche Discussion

Highlights from yesterday are the large avalanches reported from the Swan Range and southern Glacier National Park. Here are some common characteristics of these avalanches:

  •  They ranged in size from Large (D2.5) to Historic (D4).
  • They are all recent (less than 48 hours old). 
  • These failed at upper elevations on west, southwest, and south aspects. The one exception was a Very Large slab avalanche that failed on a northwest aspect.
  • We suspect they all failed on facets buried around the Dec. 22 crust. 

The recently reported avalanches may be a teaser for more to come today. Overnight temperatures climbed into the high 30s and low 40s at 6000 and 7000-foot weather stations. Today marks the third day in a row with no refreeze at some upper elevation stations. Meltwater is moving through the snowpack and into buried persistent weak layers. This process is causing the majority of the recent natural avalanche activity.

The snowpack has not yet adjusted to water moving through it. While this process continues to climb higher in elevation, a fair amount of uncertainty exists. The extent of natural activity is hard to predict when dealing with multiple nights of no refreeze. Although I don’t expect a widespread avalanche cycle to occur today, I would expect more very large avalanches to fail naturally. Slopes above roughly 6000 feet will be the most likely to fail. Warm weather will begin to cause meltwater to flow through the snowpack on more northerly-facing aspects, which may cause this problem to become more widely distributed.

Avalanches today will run relatively long distances. The elevated ratings at the middle and lower elevations are primarily for overhead hazards.

The snowpack will become more stable once we get through this warming event. In the meantime, keep it simple.

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