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17. Verification and Assessment of '23·7' Severe Rainstorm Numerical Prediction in North China

Author

Zhang Bo, Zhang Fanghua, Li Xiaolan, and Hu Yi

Subjects
numerical model, synoptic verification, verification, Meteorology. Climatology, QC851-999
Abstract

During the severe rainstorm in North China from 31 July to 1 August in 2023, CMA-GFS, CMA-EPS, EC-EPS, EC-HR, NCEP-GFS, CMA-TYM, CMA-MESO, and CMA-BJ are tested and evaluated using synoptic verification, threat score (TS), and MODE (method for object-based diagnostic evaluatin). The persistence and intensity of long-term heavy rainfall, as well as the area and intensity of short-term heavy rainfall, are tested and analyzed for their effectiveness over time. Results indicate that the cumulative precipitation predicted by EC-EPS may exceed 100 mm for 14 days in advance, but there is no prediction ability for extreme heavy precipitation above 600 mm. EC-HR forecast for the location of precipitation is generally accurate up to 8 days in advance. In the short term, the daily precipitation intensity forecast by CMA-BJ closely matches the actual situation, indicating its significance in predicting precipitation extremes. The average and maximum precipitation values of CMA-GFS, EC-HR, and NCEP-GFS in the areas with concentrated heavy precipitation are lower than actual values. CMA-GFS doesn't perform very well while EC-HR is closer to the actual situation. CMA-GFS, EC-HR, and NCEP-GFS models all provide inadequate forecasts for the persistence of heavy rainfall. However, EC-HR has a relative advantage in predicting persistent precipitation 8 days in advance. TS of CMA-BJ is highest for precipitation forecasts above 50 mm and 100 mm. EC-HR and CMA-TYM precipitation forecasts above 50 mm are relatively stable. From the daily MODE results of the precipitation concentration period from 29 July to 31 July, it is evident that EC-HR exhibits a northward predictive characteristic, while the prediction of CMA-BJ is slightly southward. The forecasting ability of CMA-GFS is insufficient, and forecasts from NCEP-GFS and CMA-MESO are not stable. The high-pressure system in North China has a significant impact on the precipitation. EC-HR model forecasts the formation and reinforcement of a 500 hPa high-pressure system 3 to 4 days earlier than CMA-GFS and NCEP-GFS models. It also surpasses both in predicting the precise location and strength of intense precipitation. Additionally, EC-HR model predicts the emergence of a 925 hPa low-pressure trough and a low-level jet 7 days in advance. However, it underestimates the intensity of the trough and jet system, with the actual location being to the west to north. CMA-GFS and NCEP-GFS underestimate the impact of the Taihang Mountains on easterly winds, leading to significantly lower precipitation forecasts. The analysis of the deviation in the 36 h precipitation forecast for 30 July also shows that EC-HR has weak predictions for low-level wind fields, trough positions, and convective precipitation, resulting in a weak intensity of heavy precipitation and a west-north precipitation area.

Published
2024
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