Diagnostic analysis of heavy snow in February 2009 and its forecast error in Shenyang

Based on MICAPS(meteorological information comprehensive analysis and process system) data and meteorological data from automatic stations,the synoptic situation and relative physical field of heavy snow on February 12-13,2009 in Shenyang were analyzed.The results indicate that the stacking of south and north ladder troughs in 500 hPa and integration of ground Mongolia cyclone and Jianghuai cyclone are the main reasons forming the heavy snow.The heavy snow occurs in large vorticity area of 850 hPa and large divergence area of 200 hPa.The middle and lower convergence and upper divergence in troposphere provide favorable power for the heavy snow.The low-level jet plays not only the vapor source of heavy snow area,but also the trigger source of releasing convective instability energy.There is the thermodynamic instability with the cold and dry upper level and the warm and wet lower level in heavy snow area.The conversion between rain and snow are related with temperature of 850 hPa,temperature advection and ground temperature.The heavy snow intensity,starting and ending times of precipitation,starting time of rain to snow are predicted accurately,except the amount of snow and depth of snow cover.