Nowcasting Challenges During the Beijing Olympics: Successes, Failures and Implications for Future Nowcasting Systems

A Forecast Demonstration Project (B08FDP) took place during the summer of 2008 that included the period of the summer Olympic Games in Beijing China. This demonstration was sanctioned by the World Meteorological Organization World Weather Research Program. The focus was on forecasting convective storms for the nowcasting time period (0-6 hours). The demonstration included state-of-the-art forecast systems from Beijing, Hong Kong, Australia, Canada and the United States.

The metropolitan area of Beijing is on a flat plain located at the foot of a mountain range, Yan Shan Mountain, which extends west and north of the city. Beijing is at an altitude of only 30 m and is open to the south and east to the influx of very warm moist air. Significant forecast challenges present themselves in the vicinity of Beijing in response to this very humid air impinging on the nearby mountains. Thunderstorms frequently initiate over the mountains and move towards Beijing. Sometimes these storms dissipate on reaching the foothills and other times grow and organizing into major squall lines. A variety of boundary layer convergence lines frequent the plains and play a significant role in storm initiation and evolution.

Initiation and dissipation in close proximity to Beijing meant that radar echo extrapolation techniques were often unreliable. Very short period numerical model forecasts were not well suited to predicting the convective storms since they were strongly influenced by local terrain. However, at the same time, the human forecaster who had a good understanding of local influences and experiences with high resolution data sets showed skill in nowcasting these events. This includes past experiences in studying the movement of convective storms from the mountains to the plains and the initiation of storms by localized boundary layer convergence lines.

Examples of thunderstorm initiation and evolution will be shown for a variety of forecasting challenges that occurred during the B08FDP. Based on B08FDP experience implications for development of future nowcasting systems will be presented.