Abstract:Using observed data of fifteen Beijing automatic weather stations during June 1 2008 to May 31 2009, the forecasting performances of Beijing rapid update cycle of assimilation forecast system (BJ RUC) to the air temperature, relative humidity, 1 h rainfall and the wind speed were analyzed in detail. The results showed that the meteorological elements of BJ RUC system had a very good consistency with the corresponding observed data. The forecast accuracy rate of ±1℃ error to the 2 m temperature was from 0.2 to 0.5, and even higher if with ±2℃. The performance to the 2 m temperature did not change obviously with the forecast range, which was closely related to seasonal and diurnal variations. The forecast accuracy was better in spring and autumn than in summer and winter, and was better in nighttime than daytime. In general, the temperature forecasted by BJ RUC system was often higher in daytime and summer. The relative humidity of BJ RUC system was lower than observation, and usually, it was lower in daytime of summer and higher in nighttime of winter. The BJ RUC system has a good performance of raining or shine to 1 h rainfall. Relatively, the accuracy rate to the rain was lower during afternoon to the evening, which may be related to the convective weather. The BJ RUC system has a different performance to different meteorological stations. Relatively, the forecasting performance was better on the plain area than the station of high altitude. For example, among fifteen stations, the accuracy rate of Beijing was the highest, and which of Yanqing Station is the lowest. To the different station, the performances of various meteorological elements were different. For instance, there had a most obvious difference to the temperature, which was maybe caused by the elevation underestimation of BJ RUC system.