Item: APRIL-FOOLED IN THE FLATHEAD: THE HAZARD OF LATE-SEASON PERSISTENT WEAK LAYERS
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Title: APRIL-FOOLED IN THE FLATHEAD: THE HAZARD OF LATE-SEASON PERSISTENT WEAK LAYERS
Proceedings: International Snow Science Workshop Proceedings 2023, Bend, Oregon
Authors:
- Cameron J.Johnson [ Flathead Avalanche Center, Hungry Horse, MT USA ]
- Blase A. Reardon [ Flathead Avalanche Center, Hungry Horse, MT USA ]
Date: 2023-10-08
Abstract: The Flathead Avalanche Center in northwest Montana has seen a spike in late-season near-misses and accidents. Surprisingly, many incidents have involved professional snow workers. April now ranks as the month with the second highest tally of incidents in the region (10), behind only February (29; 2017-2023). We examine meteorological and snowpack data leading to the events. The avalanches released on near-surface persistent weak layers. We conclude that the antecedent weather conditions are precipitation-free periods and diurnal melt-freeze cycles that occur during atypically dry conditions. These conditions are favorable for producing near-surface persistent weak layers. Backcountry riders often adopt an "open-season" mindset during these periods. When snowfall returns, a persistent slab avalanche hazard develops rapidly, yet riders may not adjust their mindsets with the same speed, leading them to misidentify avalanche problems and rely on mitigation tactics inappropriate for the conditions. A similar inertia may leave forecasters reluctant to add Persistent Slab avalanche problems or increase danger ratings. We conclude with recommendations for how the regional avalanche centers might adjust messaging to prevent similar accidents.
Object ID: ISSW2023_P2.16.pdf
Language of Article: English
Presenter(s): Cameron J. Johnson
Keywords: avalanche accidents, near-surface persistent weak layers, decision-making
Page Number(s): 736 - 740
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