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Complementary observations aid identification of the mountain rain-snow transition elevation
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  • W. Tyler Brandt,
  • Forest Cannon,
  • Ava Cooper,
  • Luca Delle Monache,
  • Kayden Haleakala,
  • Benjamin J Hatchett,
  • Bruce McGurk,
  • Ming Pan,
  • F. Martin Ralph
W. Tyler Brandt
Scripps Institution of Oceanography

Corresponding Author:[email protected]

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Forest Cannon
Scripps Institution of Oceanography
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Ava Cooper
Scripps Institution of Oceanography
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Luca Delle Monache
University of California San Diego
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Kayden Haleakala
University of California Los Angeles
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Benjamin J Hatchett
Desert Research Institute
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Bruce McGurk
Self-employed
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Ming Pan
University of California San Diego
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F. Martin Ralph
SIO
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Abstract

The elevation of the mountain rain-snow transition is critical for short-term hazard forecasting and longer-term water supply considerations. Despite the transition’s importance, direct in-situ observations are rare. Here we present two new methods that utilize “anomalous” snow observations to detect rainfall during rain-on-snow: (1) a mass fluctuation at snow pillow sites, and (2) inflated remotely sensed snow grain sizes. Using auxiliary data, we show snow pillows respond to rain-on-snow with distinct perturbations that appear as pulses, collapses and declines within the snow water equivalent. We use these responses to identify mountain-scale rain-snow transitions across California’s Sierra Nevada. We also show how a threshold approach (>200 mm) for remotely sensed snow grain size can identify rain-on-snow as snow grain sizes artificially inflate due to a liquid water film. While the methods are not predictive, if paired retroactively with hydrometeorological models, these new methods have the potential to improve predictive streamflow capabilities.