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Abstract This study examines the mesoscale structure and evolution of a polar low associated with a marine cold-air outbreak (MCAO) on 2 April 2024 over the Norwegian Sea. As part of the Cold-Air Outbreak Experiment in the Subarctic Region (CAESAR), the National Science Foundation National Center for Atmospheric Research C-130 aircraft equipped with an array of in situ and remote sensing instrumentation, including profiling radars and lidars, traversed this polar low five times, yielding detailed vertical transects of clouds and precipitation. This polar low was rather shallow and formed in the wake (not at the leading edge) of an MCAO. Observations and output from an operational convection-permitting model reveal that the polar low developed in the lee of an island, Svalbard, under deep northerly flow that roughly aligned with surface-driven baroclinicity. The polar low was marked by a region of surface-driven, mostly open-cellular precipitating convection, and a separate region of deeper stratiform clouds driven by moist-isentropic ascent in an area of suppressed surface heat fluxes. The confluence of a cold air mass from the northeast, only briefly exposed to open water, with a more mature, warmer MCAO air mass with a deeper well-mixed boundary layer previously exposed to high surface heat fluxes over the Fram Strait led to convergent, cyclonically sheared boundaries with enhanced convection. These convergent boundaries emerged as cyclonic potential vorticity streamers generated frictionally by Svalbard’s terrain, became more intense by diabatic heating in clouds, and were transported downstream into the polar low. Significance Statement Polar lows are small, intense cyclones that may cause havoc with maritime transport and may bring strong winds and heavy snowfall to coastal areas. While they are most common across the far northern Atlantic Ocean, they also occur over other high-latitude oceans. Their predictability is hampered not only by the lack of measurements at high latitudes but also by a poor understanding of their vertical structure. An airborne field campaign was conducted in early 2024 to better understand clouds in marine cold-air outbreaks, including polar lows. This study combines profiling radar and lidar data collected aboard an aircraft with operational high-resolution model data to unveil fine-scale cloud and precipitation structures of a polar low in unprecedented detail.