Imminent Localized Precipitation Preceded by a Surge in Cloud‐Base Descent and Reflectivity

The nowcasting of localized precipitation (LP) is often limited by insufficient observation of the vertical cloud evolution preceding rainfall. Here we systematically tracked rapid cloud development within 2 hr before LP onset, utilizing cloud data collected in 2024 from the millimeter‐wavelength cloud radar network across China, together with other meteorological data. Results reveal a coherent precursory signature from 40 down to 20 min prior to precipitation onset, characterized by a lowering cloud base, intensifying radar reflectivity, and enhanced turbulence intrusion into the cloud layer. This synergy creates a positive feedback mechanism that accelerates the collision‐coalescence process. Crucially, a simultaneous surge in cloud‐base descent rate (∼240 m/min) and reflectivity (10–20 dBZ) within the final 20 min provides a robust early warning signal for LP onset. These findings underscore that integrating cloud precursory information is essential for improving the accuracy of precipitation nowcasting.