Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Yesterday (Sunday), there were several human-triggered avalanches, and two people were caught and carried. Avalanches were remotely triggered, and some propagated wide distances. Expect avalanches to behave similarly today. Give steep slopes that face west-north-east a wide margin for error to allow the snowpack time to adjust. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Reports of unintentional and intentionally triggered avalanches continued to trickle in from yesterday. Several human-triggered avalanches were large enough to bury, injure, and kill a person. Signs of whumpfing collapses, shooting cracks, and unstable snowpit tests were also common themes in observations. 

    We transitioned to a Persistent Slab problem because of travel advice, and the type of weak layer avalanches are failing on. Avalanches that propagate wide distances and wrap around terrain features require wider margins for error. Slabs may be sensitive to the weight of a rider for a longer period of time due to the weak layer they rest on. It is a good time to have a "stepping back" mindset and allow the snowpack time to adjust. Aspects that face south do not have the same snowpack structure that recent avalanche activity occurred on. 

    (4/2/2023)

    Slide was triggered from a 32 degree ridgeline. The slab propagated roughly 600 feet and wrapped into two separate drainages. 

    Photo: Cam

Avalanche Discussion

A recent storm divided our forecast area into two different teams. Team Flathead/Glacier National Park led the charge with roughly 12 inches of storm snow. Team Whitefish and Swan Range came in last with roughly 2 to 4 inches of snow. Unfortunately, team Flathead/Glacier National Park also took the lead yesterday (Sunday) with the most human-triggered avalanches. Two avalanches resulted in people getting caught and carried in large slides, and another avalanche resulted in a close call. The amount of recent snow plays a key role in the avalanche problems and variability among the forecast zone.

Flathead Range/Glacier National Park

We transition to a Persistent Slab Problem in the Flathead Range/Glacier National Park due to travel advice and the grain type that avalanches are failing on. More snow fell, which resulted in avalanches failing in wind-sheltered and wind-loaded terrain. Although slabs are relatively soft, they are behaving more like a Persistent Slab than your run-of-the-mill storm snow avalanche problem. For example, my party triggered an avalanche that propagated 600 feet wide, wrapped around a sharp ridgeline, and put debris down into two separate drainages (observation). Other parties remotely triggered avalanches, with one slide stepping down to a deeper buried weak layer (observation). 

We are uncertain how long this problem may linger, but we suspect avalanches will remain reactive to the weight of a person for the near future. 

Whitefish Range/Swan Range

Generally speaking, not enough snow fell to form a slab in the Whitefish Range and the Swan Range. However, sustained winds drifted the few inches of snow into small slabs on the downwind side of ridges and gullies. Slabs of drifted snow may still be reactive to the weight of a rider, but likely small in size and confined to wind-drifted features. I would expect to see slides similar to the ones found in this observation. These should be easy to manage by giving them a wide berth and by sticking to wind-sheltered slopes. 

We received no observations from the Swan Range, giving us a slightly higher degree of uncertainty there. IF you find more snow than expected, dial back your terrain choices and give steep slopes a wider margin for error. 

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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