Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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

On Sunday, there were several human-triggered avalanches. Signs of unstable snow, such as whumpfing collapses, were reported yesterday (Monday). These signs tell us it is still possible to trigger an avalanche and to stick to lower-angle slopes. Recent avalanche activity and signs of unstable snow primarily occurred on northerly-facing aspects. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    On Sunday, several human-triggered avalanches were large enough to bury, injure, and kill a person. A triggered avalanche today may still propagate wide distances and wrap around terrain features. Slabs will be thicker and more dangerous in wind-drifted areas.

    If traveling on aspects that face northwest-north-east, the safest bet is to keep slope angles low. Give steep terrain above you a wider margin for error since avalanches were remotely triggered in the past 48 hours. So far, we have no reported slab avalanches from aspects that face south and west. This may provide options for steeper riding on those aspects. Whumpfing collapses and shooting cracks are signs to resort to safer terrain options. 

    (4/2/2023)

    Photo from an unintentional triggered avalanche. The crown height measures 34 inches in this location. This was the thickest part of the slab. The average crown depth was 12 inches. 

    Photo: Cam

Avalanche Discussion

On Friday and Saturday, a winter storm brought 8 to 12 inches of snow to the Flathead Range/Glacier National Park forecast zone. The Swan Range and Whitefish Range received only 2 to 4 inches of snow. With this snowfall came moderate wind speeds, which are ripe speeds for drifting snow into thicker slabs. Since then, we have received numerous reports of natural avalanches, human-triggered avalanches, and signs of unstable snow. Here are a few noteworthy observations from each forecast zone (Flathead, Glacier National Park, Whitefish, Swan). 

On shaded aspects, storm snow fell on a weak layer of facets. This sugary snow is the culprit for recent avalanche activity. Unfortunately, this weak layer may be slow to heal, which is one of the reasons we transitioned to a Persistent Slab avalanche problem in the Flathead Range. Another reason is that avalanches are breaking in surprising ways by wrapping around terrain features and being remotely triggered. This requires a wider margin for error by putting more space between you and the steep slopes that harbor this structure. This structure is primarily found on northerly aspects above roughly 6000 feet.

On south and west-facing slopes, recent snow fell on a melt-freeze crust. Observations suggest that it is less likely to trigger a slab avalanche on those aspects. However, if you plan to travel on solar aspects today, keep an eye on cloud cover and surface warming. If the sun sticks its face out longer than expected, plan to see some rollerballs and small wet loose activity out of steep rocky areas. This will be more common in the Flathead Range where more snow fell. A sun crust may already exist on some solar aspects.

Continue to steer around signs of wind-drifted snow in the Swan and Whitefish Ranges. Slabs of drifted snow sit on weak snow that will be slow to heal. Pockets of drifted snow should be easy to identify by their textured appearance. 

FAC will issue daily forecasts through Easter Sunday, April 9. Following this, we will give snowpack updates several times a week through April if conditions dictate. 

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