Performance Evaluation of CMA-BJ V2.0 System for Precipitation Forecast in North China

To meet the requirement of numerical weather forecast for local severe convective weather, especially disastrous weather and extreme weather events, based on CMA-BJ V2.0 system, many works have been implemented, including increasing the model vertical layer to 59 layers, testing different physical parameterization schemes, assimilating unconventional local dense data such as wind profile radar and the near surface data, developing rapid cycle technology, and applying the incremental analysis update initialization technique of large-scale dynamic hybrid scheme for forecast field. By integrating all the jobs mentioned, the rapid analysis and forecast system CMA-BJ V2.0 has been established and put into operational run since June 2021 with 1 h time interval. A large number of tests and evaluations on multiple versions of the CMA-BJ numerical forecast system have been carried out. It is confirmed that the forecast skills of the model are improving year by year. There are still some problems in the forecast, such as heavy precipitation, high percentage of effective precipitation hours, and large deviation in the forecast of weak precipitation. Based upon 24 h precipitation forecast and 24 h hourly precipitation forecast information in North China on each day of the 2021 flood season (June to September), the comprehensive performance of CMA-BJ V2.0 forecast system with different resolutions (3 km and 9 km) is carefully evaluated and analyzed in terms of accumulation, percentage of effective precipitation hours, precipitation intensity, and daily cycle characteristics. The results show that both 9 km and 3 km resolutions can forecast the precipitation level and the rainfall area well and capture the regional distribution characteristics of precipitation with daily average precipitation greater than 8 mm well, but the forecast of precipitation level is larger than the observation. The forecast of hourly precipitation and the daily cycle of percentage of effective precipitation hours in North China is generally consistent with the observation, but the forecast of the peak in the evening is strong. The hourly precipitation is overestimated due to false alarms. For 3 km resolution forecast, the trend of percentage of effective precipitation hours is more similar to the observation. The magnitudes are closer to the observation than 9 km resolution forecast. 9 km resolution forecasts have better forecasting ability for weak precipitation processes, while 3 km resolution forecast is better at strong precipitation processes. The forecast results of a typical precipitation case in North China on 21 July 2021 are consistent with the test results of the average of the whole flood season: The model of both resolutions can better forecast the precipitation process, but the amount and percentage of effective precipitation hours is overestimated.