Item: WHY SWE MATTERS: WHEN HIGH SNOW DENSITY HIDES HIGH HAZARD
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Title: WHY SWE MATTERS: WHEN HIGH SNOW DENSITY HIDES HIGH HAZARD
Proceedings: Proceedings, International Snow Science Workshop, Whistler, BC, Canada, 2026
Authors:
- Sara Bogert [ Mammoth Mountain Ski Patrol, Mammoth Lakes, CA, USA ]
Date: 2026-09-28
Abstract: Mammoth Mountain in the Sierra Nevada Range, California, USA, is characterized by extreme wind speeds and intense snowfall events that produce high-density dry snow. In an attempt to find the largest 24-hour snow event possible, I looked at 24-hour snowfall records and 24-hour snow water equivalent (SWE). This analysis showed that intense snow loading periods from Mammoth met or exceeded the SWE from several U.S. state snowfall records but had half of the snow height of those records. For these storms, forecasting approaches focused on height of new snow (HN) can underestimate hazard. Defining a SWE-based forecasting threshold for extreme loading is essential to characterize unusual hazard in this climate. Several recent severe incidents at Mammoth Mountain occurred within 36 hours of registering 4.25 inches or greater 24-hour SWE, a value close to the 4.7 to 5.71 inch SWE range from the snowfall records. Based on these findings, I propose using 4.0 inches of 24-hour SWE as a forecasting threshold at Mammoth and in similar climates to identify extreme loading that poses potential great risk to avalanche practitioners.
Object ID: ISSW2026_P2.47.pdf
DOI: https://doi.org/10.15788/1790099019
Language of Article: English
Presenter(s): Sara Bogert
Keywords: 24-hour SWE, heavy snowfall, extreme snow loading, snowfall records
Page Number(s): 1685 - 1692
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