Complementary observations aid identification of the mountain rain-snow
transition elevation
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.