Abstract:
The rapid-refresh integrated nowcasting system, as an important supplement to the numerical weather prediction (NWP) models, can improve the spatiotemporal refinement level of weather forecasts. This paper provides an overview of Zhejiang Integrated Nowcasting System from the perspectives of analysis and forecasting methods, data and operational process and evaluation results. The system starts with an NWP short-range forecast as a first guess and combines refined terrain data and multi-source observations such as weather radar and automatic weather station data to generate a high-resolution real-time analysis field. Vector extrapolation, dynamic downscaling and weighted fusion techniques are subsequently applied to produce nowcasting outputs. The system can provide multi-element real-time analysis and 24 h forecast for Zhejiang Province at a 500 m spatial resolution, with 10 min rolling updates. Evaluation results during the Hangzhou Asian Games (September-October 2023) demonstrate that the real-time analysis field accurately reproduces observations and effectively captures complex terrain effects. Nowcasting products exhibit enhanced timeliness and accuracy, with the most significant added value observed within the first 6 h. Compared to the NWP output, the root mean square errors of temperature, wind speed, and relative humidity for the first 6 h are reduced by 26%, 23% and 21%, respectively. Significant improvements in precipitation forecasts are most pronounced within the first 3 h, with the threat score (TS) obviously higher than NWP results.