A Climatology of Narrow Cold-Frontal Rainbands in Southern California

Narrow cold-frontal rainbands (NCFRs) produce short-duration, high-intensity precipitation associated with flash flooding and debris flows in Southern California, including the extremely destructive 2018 Montecito event. This manuscript presents the first known catalog of NCFR events in this region during winter seasons 1995-2020. A manual approach was used to identify NCFRs in radar imagery, supported by rain gauges and atmospheric reanalysis products. In total, 94 NCFRs were observed, with an average of three landfalling events occurring per water year. Propagation and impacts of these NCFRs were also investigated. Composite analyses of synoptic conditions reveal similarities across events; however, individual NCFRs exist on a spectrum of atmospheric conditions, precipitation intensity, and associated hazards. This regional record serves as a control dataset for the development of an objective identification algorithm and supports the evaluation and improvement of forecasting procedures. Methods established here are transferrable to other mid-latitude regions with limited radar coverage.