A Climatology of Narrow Cold-Frontal Rainbands in Southern California

Narrow cold-frontal rainbands produce short-duration (<1-hr), high-intensity precipitation associated with flash floods and debris flows in Southern California, including the extremely destructive 2018 Montecito event. Prior research describes development, predictability, and associated hazards of these bands, though no known long-term record of their occurrence and climatological characteristics exists within the United States. This study provides the first known catalog of narrow coldfrontal
rainbands during the winter seasons of 1995–2020 in Southern California, and explores characteristics of these features such as frequency, movement, and the large-scale meteorology that drives them. Events were documented manually using rain gauge observations, radar data, and output from atmospheric models. In total, 94 rainbands were documented during the study period, with an average of three landfalling events occurring in Southern California per water year. The intensity and impacts across the recorded events varied, though common weather patterns, including strengthening cyclones near the California coast, were associated with the documented events. This catalog supports weather-forecasting efforts as well as the future development of an automated detection algorithm.