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Based on the conventional, microwave radiometer,and wind profiler data, the causes of a snowy weather event occurred on 7 February 2007 in Beijing are analyzed. The analysis of the circulation situation shows that the largescale circulation situation was favorable to the snowy weather during the eastward shifting of the middle troposphere convergence system, such as the strong warm southerly airflow and nearsurface conditions, etc, which are similar to the classical model of snowing in Beijing. The causes of the false precipitation prediction for the most part of Beijing include the filling of the inverted trough resulted from the weak southward cold airflow, the weak ascending current in the convergent system in PBL, and the relatively high and thin wet layer. The main reason for the false snowfall prediction is that the location and intensity of weather systems from NWP have obvious bias and longer lead time, and it is difficult for forecasters to judge the weather situation. The precipitation occurred at some stations in the eastern Beijing is mainly induced by the shortterm returning airflow in the condition of abundant vapor while the passing of an upperlevel trough with poor dynamic lifting. Under the favorable condition of abundant vapor provided by the warmwet air flow from south, condensation occurred easily at relatively high altitudes, which is the main reason of snowfall at some highelevation stations over Beijing.