Based on the conventional meteorological data and 4 times daily NCEP reanalysis data,the causes of rain changing snowstorm in Liaoning during February 12-13 of 2009 were discussed.The low-level jet conditions,temperature conditions and coupling mechanism of water vapor and dynamics of heavy snow were diagnosed and analyzed.The low-level jet provided abundant water vapor for this process.The convergence at low level,divergence in the upper troposphere and strong ascend movement provided dynamic conditions for the snowstorm.The wedging of cold air was the chief cause of rain changing snow.The strongprecipitation area corresponded to the moist potential vorticity well.
