Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Roughly 2 to 5 inches of snow fell in the Swan and Flathead Ranges overnight, which helped refresh snow surfaces and make for dust on crust-like conditions. Watch for small loose dry avalanches during the morning hours that will transition to wet loose as the day progresses. Keep an eye out for overhead hazards and manage your sluff if conditions lead you into steep terrain. Select slopes free of terrain traps where a small avalanche can have large consequences. 

Problemi valanghivi

  • Loose Dry

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

    Overnight temperatures dropped below freezing above 5000 feet throughout the forecast area, which re-froze the snow surface. Following the drop in temperatures, roughly 2 to 5 inches of snow fell in the Flathead Range, and I would expect similar accumulations in the Swan Range. Clearing skies and warming temperatures will spur a round of small natural avalanches. These will likely start as loose dry and transition to loose wet throughout the day. These avalanches should not be large enough to bury you, but you will want to use defensive riding strategies to avoid getting knocked over or caught in steep and consequential terrain. Point releases from steep rocky areas and rollerballs are signs that the loose snow avalanche problem is taking on wet avalanche characteristics. 

    (3/27/2021) Tree bomb triggering roller balls is a sign of an impending wet loose cycle. The first sign that the loose dry avalanche problem is taking on wet characteristics.

  • Persistent Slabs

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

    It is progressively more and more unlikely to trigger a very large avalanche failing on weak faceted snow 2 to 6 feet below the surface. The most likely location of triggering an avalanche-like this is on slopes that lack a hard and supportable melt-freeze crust under the new snow. Aspects that face northwest to the northeast at upper elevations lack this kind of crust. Steer away from slopes that are rocky with variable snow depths that appear complex to navigate. Avoid steep convex rollovers where a rider is more likely to collapse the weak layer leading to a large avalanche. A cornice fall will be the most likely natural trigger. 

    (3/16/2021) A hard slab of snow sitting over buried persistent weak layers.

Avalanche Discussion

Remote weather stations in the Flathead and the Swan Range show temperatures that dipped below freezing starting at 7 pm last night. The Whitefish Range lucked out on Sunday and remained cool throughout the day, which kept surfaces frozen since Saturday. Precipitation overnight at the Tunnel Ridge station in the Flathead Range is picking up roughly 4 inches of snow by 5 am. Noisy Basin in the Swan Range shows unreliable and variable data, and the Whiteish Range is mostly getting missed by precipitation. Expect accumulations to vary from basin to basin today and track how much snow fell overnight in the drainage you are in.

The weather forecast shows clearing skies and freezing levels to reach up to roughly 7000 feet by late afternoon. This will start a round of small loose snow avalanches that should be easy to manage. Look for small point releases out of steep, rocky terrain and if you begin to see rollerballs, expect these dry sluffs to take on wet loose characteristics. This should be your sign to move quickly through areas with overhead hazards and be extra cautious of what type of terrain is below you. 

An overnight re-freeze will make cornice fall less likely today. Although we removed them from the list, maintain good travel protocols, and give ridgelines a wide berth. Travel further back from the ridge than you feel comfortable with and give the slopes below them a margin for error. These cornices loom over the terrain that is most likely to harbor weak snow buried 2 to 6 feet deep. The most likely trigger for a persistent slab avalanche is a falling cornice.

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