Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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

In sintesi

Dangerous avalanche conditions are developing due to new snow overnight and throughout today. The danger may rise as the day progresses. Fresh slabs will be reactive to the weight of a rider and their machine. Steer around areas of wind drifted snow or where the snow surface is cracking beneath you. Choose terrain less than about 35 degrees in steepness for a safer, more enjoyable experience.

Problemi valanghivi

  • Wind Slabs

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

    On Saturday, impressive southwest winds transported what remained of our mid-week snowfall onto leeward aspects. Overnight snow, along with today's additional snowfall, will refresh fetches and be available for transport. Wind speeds will continue to be strong enough to form fresh slabs below ridgelines, downwind of saddles, and on the sidewalls of gulleys. As an arctic front enters our area this afternoon anticipate shifting winds drifting snow onto westerly and southerly aspects. Note blowing snow as you gain elevation as a clue that the wind slab machine is firing on all cylinders. Cracking in the surface snow is a sign of instability, directing you to seek out safer slopes sheltered from the wind.

    (2/18/2022)

    Riders intentionally triggered this small wind slab on a north-facing test slope at 6400 feet.

    Photo: Alex

  • Storm Slabs

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

    Areas in the Flathead Range along with southern and central Glacier Park received around 6 inches of snow overnight, with possibly an additional 6 - 8 inches today. If the forecast verifies, we may develop a storm slab problem in areas sheltered from the wind. The development of this problem is dependent on today's snow totals and snowfall intensity. Look for cracking beneath you or your machine. Utilize hand pits and small test slopes to see how well the new snow bonds to the underlying layer. If you notice any red flags, choose slopes less than 35 degrees in steepness that have runouts free of surface obstacles.

    (2/16/2022)

    Loose dry and soft slab avalanches. These are more likely to fail naturally during times of heavy precipitation rates. 

    Photo: Cam Johnson

  • Persistent Slabs

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

    An extended period of mild weather continues to strengthen weak layers 1-2 feet below the surface. Buried surface hoar and facets may still be affected by the weight of a rider or their snowmachine in locations where a supportable surface crust does not exist. Continued propagation in snowpit tests confirms we are not out of the woods quite yet. If you choose to recreate in terrain on the north half of the compass, select planar slopes free of convexities to minimize your chances of triggering a slide. Choose areas with clean runouts free of surface obstacles that may limit the extent of trauma and burial if you are unlucky enough to awaken this layer.

    (2/8/2022)

    Very large (D3) avalanche that likely failed on buried persistent weak layers on 2/6 or 2/7. 

    Photo: Alan Davis

Avalanche Discussion

This morning's snow totals are a little underwhelming in most locations. Central Glacier Park and the corridor between John F. Stevens to Marias Pass picked up around 6 inches of snow overnight. At the same time, the Swan Range and the Whitefish Range have only received a couple of inches as of 0500 Sunday morning. Snow is still on track to affect the area through today with up to 6 - 8 inches of additional snow. Southwest winds will remain strong enough to transport the storm snow into fresh slabs on typical leeward aspects. An Arctic air mass will enter the area later today, dramatically dropping the air temperature and bringing breezy north to east winds. There may be a bit of enhanced snowfall as the front interacts with today's precipitation, but then the cold air will shut down the precipitation overnight.

The avalanche danger has risen due to overnight snowfall and today's anticipated snow. The given is that wind slabs will be larger and more reactive to the weight of a rider than what we experienced over the past few days. The unknown is the storm slab problem. We have added this to the avalanche problems due to the expected snowfall throughout the day. If the forecast does not verify, this problem may not develop or perhaps only in isolated areas. We generally don't list both wind and storm slab in a forecast but today seems worthy. 

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