Abstract:This paper analyses the forecast deviation of the first snow in 2016 in Beijing using EC reanalysis data and wind profiling radar from 19 to 21 November 2016. The conclusions are as follows. (1) The deficiency of “cold wedge”, the location of shear line at 850 hPa by south and the lack of whole layer precipitable water caused the total snowfall amount less than that of the forecast. (2) There are four reasons for the less snowfall amount in urban areas of Beijing. That is, the convergence of water vapor flux was weak, the time for rain to turn into snow was 3 hours later than that of the forecast, the saturation in the layer from -18 to -9℃ was insufficient, and the precipitation weather system had passed through Beijing after rain turned into snow. (3) The slow falling of the 0℃ layer height was due to the failing formation of “cold wedge”, and the strong warm advection in low levels. At the same time, the similar weather examples are compared in this paper. When it refers to the phenomenon of rain into snow and the insufficient saturation at high levels, the 0℃ layer height should still be considered in forecasting the time of rain into snow. When the 0℃ layer height drops to lower than 100 m, rain can turn into sleet and snow.