Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

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

In sintesi

Avoid upper elevation slopes greater than 35 degrees where you may find wet and unconsolidated snow. This snow can be triggered by a person and can be hard to escape once moving. Keep glide cracks and cornice fall in mind, and continue to stay out from under slopes where these hard-to-predict hazards exist.

Problemi valanghivi

  • Cornices

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

    With ongoing warming temperatures, keep an eye out for anomalous events like cornices fall and even glide avalanches. Cornices can fall without warning and can have unexpected consequences, including triggering very large avalanches. They can break further back than anticipated. When traveling on ridges, make sure to stay well away from the edge and look for clues like rocks or trees sticking out of the snow to indicate where the ridgeline actually is. Stay out from under cornices and be sure to only stop and re-group in areas free from overhead hazards.  

    (4/1/2024)

    Large cornices on ridgelines may fail with recent warming and rain on snow over the last 24 hours.

    Photo: Austin Seback/Sarah Williams

  • Loose Wet

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

    You could trigger wet avalanches and they may even run naturally as wet precipitation adds up by the second half of the day. Expect the largest ones near and above treeline on shaded northwest through northeast aspects where the upper elevation snowpack previously remained dry and cold.

    Pay attention to how much the surface snow is gone from dry to wet and note increases in ski penetration as you travel thoughout the day. You can use small test slopes to confirm how reactive the wet snow is to the weight of a rider or machine.

    (3/2/2024)

    Wet loose debris likely caused by recent rain on snow at low and mid elevations. 

    Photo: Mark Dundas

Avalanche Discussion

This week, sunshine with warm temperatures and light rain with overcast skies has changed the snowpack dramatically. Many weather stations stayed above the freezing mark for several days earlier in the week. Mid and upper elevation Northerly slopes may have finally met their match with this recent warming trend, and the surface snow has transitioned from dry to wet. 

Overnight, temperatures just dipped below the freezing mark at several mountaintop locations, and winds shifted from southerly to east/northeast. Today looks to be another dynamic day across the forecast area. We can expect a mix of rain and snow at various points throughout the day. It is possible we may see up to a few inches of snow at upper elevations by early evening. If you find yourself in an area with several inches of accumulated new snow, check how well the new snow is bonding by using a quick hand shear or small test slopes. Poor bonding and cohesive slabs should direct you to lower angle sheltered slopes.

Yesterday (Wednesday), Cam and I traveled to Skiumah Lake and confirmed our suspicions about the transition from dry to wet snow. We found many new wet loose avalanches on the north side of Mt. Penrose (obs). Cooler temperatures can be expected at mid and upper elevations today, helping to reduce the chances of wet snow avalanches as the day progresses. However, look for this problem primarily on shaded aspects that have recently been warmed for the first time this season.

A recent fatality on Mount St. Helens is a reminder of the potential harm that cornice falls can have. You can read the preliminary report here. Don't be fooled by this season's anemic lower elevation snowpack; there was still plenty of snow and wind at upper elevations to form large cornices along ridgelines across the forecast area. 

It's hard to believe it, but FAC's last daily forecast will be on Monday, April 8th 2024.  After that we will continue to issue conditions updates on Tuesdays and Fridays until May or as conditions dictate. 

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