Abstract:Based on Fujian dense automatic station data, wind profile radar data, S band dual polarization radar data, raindrop spectrum data and NCEP 1°×1° reanalysis data, the failed forecast of winter torrential rain for central and southern Fujian from 20:00 BT 21 to 20:00 BT 22 February 2017 is analyzed. The results suggest that: (1) The uncommon torrential rain happened ahead of the front, under the background of strong and long persisting low level jet, seen only once since 2000, and was not affected by the southern trough and cold air. (2) Convective systems in central and southern Fujian were independent to each other, and multiple convective systems affected central Fujian, but only two affected southern Fujian. The convective precipitation was warm rain process convection, easily causing the underestimation of rainfall intensity. (3) The water vapor came mainly from the South China Sea. Compared with heavy rain events in flood season, the low level water vapor condition was similar to that of flood season although water vapor in the whole layer was slightly weaker. Warm and wet air transport by low level jet increased the instability of stratification in rainstorm area, but the convective instability was slightly weaker than that in the flood season. (4) Divergence at upper layer coupling with low layer convergence provided favorable condition for the dynamic lifting of rainstorm areas, but the wind vorticity was not strong and there was no obvious positive vorticity column. Analysis of wet potential vorticity indicates that the heavy to trorrential rain in central Fujian was mainly related to conditional symmetric instability, resulting in the inclining ascending motion, but both convective instability and conditional symmetric instability played great roles in the rainstorm area in southern Fujian.