Characterizing Rainfall Variability Within a Series of Storms Over Northern California in February 2017

In February 2017, a series of storms with associated atmospheric rivers (ARs) made landfall in the US state of California, dropping large amounts of precipitation over the Sierra Nevada Mountains and their western foothills. The rainfall from these ARs, long, narrow bands of water vapor that transport large amounts of water vapor from the tropics to the mid-latitudes, instigated the near-failure of the Oroville Dam located at the southeastern edge of the Feather watershed outside the city of Oroville in the state's Central Valley. This case study provides a synoptic and mesoscale diagnosis of the drivers of rainfall pulses that were observed within individual storm systems that led to the Oroville dam crisis. Rain gauge, radar, satellite-based, and reanalysis data are used to identify and diagnose precipitation pulses embedded within these storms, and the local and synoptic-scale forcing characteristics attributed to these pulses are identified and described. Results are insightful for understanding how precipitation pulses propagate within larger storm systems and will expand the general knowledge of the mechanisms that drive precipitation variability from within-storm events. More specifically, understanding the drivers of within-storm precipitation pulse variability for an impactful event such as the Oroville dam crisis are important for several reasons. The compounding meteorological conditions described in this paper can be used to highlight critical uncertainties in pulse detection and prediction, provide gains in the predictive skill of extreme mesoscale precipitation pulses on changing landscapes, and generate new decision-support information to assist water and environmental resource managers in developing the next generation of adaptive management practices.