Item: TRACKING WET SNOW AVALANCHE FREQUENCY AND SEASONAL PATTERNS AT ALYESKA RESORT, GIRDWOOD, ALASKA, FROM 1968 TO 2026
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Title: TRACKING WET SNOW AVALANCHE FREQUENCY AND SEASONAL PATTERNS AT ALYESKA RESORT, GIRDWOOD, ALASKA, FROM 1968 TO 2026
Proceedings: Proceedings, International Snow Science Workshop, Whistler, BC, Canada, 2026
Authors:
- Aleph Johnston-Bloom [ Alyeska Resort, Girdwood, AK, USA ]
- Jeff Bristow [ Alyeska Resort, Girdwood, AK, USA ]
Date: 2026-09-28
Abstract: This study uses 58 seasons (1968/69–2025/26) of avalanche records from Alyeska Resort in Girdwood, Alaska, to evaluate changes in the recorded frequency, seasonal timing, and magnitude of wet loose, wet slab, and glide avalanches. The number of months per season with wet avalanche activity increased significantly over the study period (slope = 0.033 months per season, standard error: 0.0104, p = 0.0025). Wet avalanches were recorded more frequently from November through February during the second half of the record, while April remained the most consistently active month. The annual frequency of Size 3 and 4 wet avalanches did not increase significantly, indicating that the clearest change was a broadening of wet avalanche occurrence across the winter rather than an increase in large events. We also used separate winter and spring CatBoost models to evaluate combinations of meteorological and snowpack variables associated with wet slab and glide avalanche days. During independent testing from 2022/23 through 2025/26, the winter model identified 9 of 13 avalanche days and the spring model identified 14 of 24. False positives remained a limitation. The results demonstrate the value of long-term operational records for identifying changes in wet avalanche patterns. They also support ongoing efforts to model interactions between weather and snowpack variables as a potential source of supporting information for operational forecasting.
Object ID: ISSW2026_O6.4.pdf
DOI: https://doi.org/10.15788/1790098635
Language of Article: English
Presenter(s): Aleph Johnston-Bloom
Keywords: wet snow, climate, avalanche forecasting, machine learning
Page Number(s): 1375 - 1382
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