| A heavy rainstorm occurred in Henan Province between 19 and 21 July,2021,with a record-breaking 201.9 mm of precipitation in 1 h.To explore the key factors that led to forecasting errors for this extreme rainstorm,as well as the dominant contributor affecting its predictability,increase awareness of uncertainty in rainfall forecasting,on the basis of analyzing the physical mechanism and key factors influencing the uncertainty of "7.20" extreme precipitation in Henan,this paper analyzed the predictability of this extreme precipitation more in depth based on convective scale ensemble forecast,and analyzed the forecast quality,the predictability of main influence system and the evolution of ensemble disturbance and spread.It provides the basis for further research on forecast capability and improvement direction of convective scale ensemble forecast.The main conclusions are as follows:(1)In the context of stable circulation such as subtropical high,continental high and typhoon In-Fa,the continuous transmission of water vapor,orographic uplift and synergies between mesoscale vortex and multiscale weather systems have contributed to the development of the "7.20" extreme precipitation process in Henan,which is strong,efficient and long-lasting.(2)The effective prediction of the strength and evolution of upper tropospheric cold vortex,middle-low vortex,and low-level jet is the key factor of the optimal member,Conversely,the prediction deviation of unstable and dynamic conditions in the lower level of the worst member leads to a decline in the forecast quality of rainfall intensity and its rainfall area.GRAPESREPS has great uncertainty in heavy precipitation forecasts caused by strong weather systems,but shows high predictability for heavy precipitation caused by topography.Compared with the ECMWF-EPS,GRAPES-REPS exhibits a better forecast ability for heavy rainfall,with some ensemble members able to better predict extreme precipitation.The intensities of the shortwave trough,upper tropospheric cold vortex,low vortex,and low-level jet stream had a higher ensemble sensitivity to heavy precipitation.(3)Convective scale ensemble prediction(CEPS)shows higher predictability of precipitation in rainfall and drop areas and can accurately describe the daily variation of precipitation in Henan Province.Compared to the worst member,the optimal member of CEPS have stronger high-level divergence and more accurate coupling between low vortex and lowlevel jet.Coupling situation at high and low altitude is conducive to predicting more accurate precipitation.However,there is time lag in the development of convective available potential energy of all members,which is not in step with the development of low vortex and low-level jet,resulting in low forecast rainfall.(4)Convective scale ensemble prediction(CEPS)accurately captured the uncertainty of high-altitude critical weather systems such as the trough,the high-pressure ridge,and the cold vortex;In the lower troposphere,the wind field disturbance of CEPS is more dependent on flow and can accurately capture the location of low-level jet.CEPS can describe the uncertainty of small-scale weather system more accurately.GRAPES-REPS needs to improve its low-level initial disturbance of potential height field and temperature field to solve the problem of decreasing after the sharp increase of spread in the early stage of model integration.The field method improves the precipitation probability of CEPS near Zhengzhou,and to a certain extent improves the predictability of extreme precipitation events in Henan. |
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