Comparative analysis of two extreme blizzard processes in Urumqi

Using conventional observation data,auto-weather station data,NCEP/FNL (1°×1°) reanalysis data,comparative analysis on the water vapor condition,instability and dynamic condition has been carried out for two extreme blizzard events happened in north slope of Tian-Shan Mountain. Results indicate the following. (1) 500 hPa high-level trough,700 hPa short wave trough and 850 hPa shear line are the common systems associated with the two extreme blizzard events. (2) In both events,there were southwest jet and -36℃ cold center on 500 hPa,and northwest jet on 700 hPa and 850 hPa. High water vapor flux and water vapor flux divergence throughout all layers provide good water vapor condition. (3) Wind field convergence and strong updraft produced by Tianshan Mountain topographic uplift give the bliz-zard events strong dynamic condition. (4) In both two events,there were southeast wind controling the upper levels over Urumqi. The inver-sion layer is favorable to accumulating unstable energy. But the different circulation situation,water vapor distribution,and energy aggrega-tion cause different snowfall thickness and urban impact.