On the night of May 21, 2023, the Jiangxi Meteorological Observatory and the meteorological stations of relevant cities forecasted that there would be a wide range of rainstorm weather in the southern part of northern Jiangxi, but only light rain occurred in reality. To explore the causes of the rainstorm false alarm, this paper uses mesoscale weather analysis, synoptic meteorological diagnosis, and statistical comparison methods to analyze the circulation background, environmental conditions, and model errors that were unfavorable for the formation of rainstorms. The results show that: (1) At 20:00 on May 21, the southern part of northern Jiangxi was located in the anticyclonic circulation to the north of the low_level shear line. The specific humidity decreased and the humid layer was shallow. There was wind speed divergence in the southwestern jet stream at 700 hPa leading to subsidence motion. Moreover, there was no pseudo_equivalent potential temperature energy frontal zone. The water vapor, dynamic, and thermal conditions were all unfavorable for the occurrence of heavy precipitation. (2) There were relatively large forecast errors in the situation field of the EC model. The position of the weather system was predicted to be more northerly, and the model failed to capture the warm ridge and mesoscale temperature frontal zone in southern Jiangxi. Thus, the intensity of convective development in southern Jiangxi was neglected, and the misjudgment that there would be heavy precipitation in the southern part of northern Jiangxi was made. The overestimated specific humidity, northward_biased vertical upward movement at 700 hPa, and overestimated CAPE value were also factors contributing to the errors in the heavy precipitation forecast. (3) The relative position of the 584 dagpm characteristic line to the actual situation and 925 hPa wind field in the boundary layer can well reflect the moving speed of the weather system, and have good indicative significance for the overall southward correction of the heavy rainfall area. The EC model accurately predicted the characteristics of wind speed divergence at 700 hPa and the triggering mechanism of boundary layer convergence in southern Jiangxi. By reducing the convective precipitation magnitude of the EC model, and paying attention to the high_temperature and high_humidity area on the south side of the 925 hPa front zone, we can effectively avoid the false alarm of rainstorms in the southern part of northern Jiangxi. These findings can provide a reference for the forecasting, early warning and correction capabilities of rainstorms in Jiangxi Province.