Sea‐breeze front (SBF) can cause dramatic changes in weather and air quality near the coast. However, the observation and forecast of its three‐dimensional (3‐D) fine‐scale structures have been challenging. Using mesoscale‐to‐large eddy simulations (LES) models and high‐resolution lidar measurement over Sendai Airport, here we perform a successful simulation of the observed 3‐D structures of an SBF for the first time. We show that frontal structures are characterized by a series of lobes (spaced ~500 m apart) aligned along the raised sea‐breeze head, where the shear between sea breeze and alongshore ambient flow aloft is evident. Local strong updrafts occur both in the frontal lobes of marine cold air and in the prefrontal warm air ascending the wedge of windward lobes. Downdrafts form behind the lifted marine cold air and trap air pollutants. These fine‐scale structures and vertical motions are repeatedly strengthened by the short‐term disturbances of gravity currents that move onshore and collide with the SBF. They are also affected by buildings and determine the detailed variations of surface winds. We conclude that advanced observation and modeling systems can potentially improve the prediction of coastal weather and environment. Plain Language Summary When sea breeze comes, it does not come gently and often brings a sudden change in winds, temperature, and air quality. The so‐called sea‐breeze front has great influence on the environment in coastal areas around the world. This work presents a major progress to reveal its fine‐scale 3‐D structures using the state‐of‐art observations and numerical models. The dynamics and evolution of the frontal structures are further linked to the disturbances of gravity current and the effect of buildings near the coast. Some differences to the known concept of idealized sea‐breeze front are also identified. We believe that the findings have significant impacts on the research community of weather forecast, numerical modeling, and coastal environment studies. Key Points Lidar observations capture well the fine‐scale 3‐D structures and evolution of a typical sea‐breeze front A novel local prediction system can reproduce frontal lobes/clefts and updrafts at high accuracy and resolution Gravity current disturbances control the short‐term variations of frontal structures, while coastal buildings affect detailed features