Analysis on the Key Factors in Causing Heavy Rain and Precipitation Forecast Deviation in a Regional Persistent Heavy Rainfall

A regional persistent, heavy rainfall occurred in the Jianghuai area, China during July 1-2, 2016. With using the data of precipitation observations, the ground observation data, satellite cloud picture data, radar data and ECMWF ERA reanalysis data (0.75 ° * 0.75 °) to analyze the key causes for the heavy rain process and the precipitation forecast deviation obviously problem. Depending on the use of the theory of geo-potential tendency equation we analyzed the rationality of the distribution of meteorological elements on the upper and lower levels, and compared the forecast results of the EC model and East China Regional Center model from both aspects of subjective and objective. We explored and discussed the thinking and judgment experience and corrections on the NWP of forecasters in this process, and the results show that position and shape of the subtropical high over west pacific are stable in the process, and the north border of the 588 dgpm area near 120°E are stable at around 29°N, with the circulation background determining the persistency of the heavy precipitation. Out flow area of the high level wind field, low-level convergence zone, the position and verticality of jet affects combinedly rainfall zone, with the divergence center corresponding perfectly to the center of heavy rain, and the jet, vertical speed rise area, the positive vorticity presenting a strong vertical distribution just around 32°N. Deviation analysis indicates that the circulation situation forecast upper than 500Hpa perform good, the lower is relatively poor. According to the upper and lower level system development theory, it can be used to a certain inspection and judgment of the low level prediction and correction with the high-level situation forecast. General weather systems tilt commonly to south from upper to lower, so once appearing the opposite situation, forecasters need to judge and determine the model forecast results about the intensity and position of the low level jet that plays a key role in correction of rain forecast.