Abstract: Using conventional meteorological observation data, regional automatic weather station data and NCEP 1°×1° reanalysis data for 6 hours in January 2018, the causes of the two heavy snowstorms in eastern Anhui on January 3—4 and 24—28 and their structural evolution characteristics, such as power, water vapor thermodynamics and dry intrusion, were diagnosed and analyzed. The results showed that the high-altitude cold trough and the low-altitude vortex shear development were the important circulation background for the formation of snowfall, the southwest low-altitude jet zone of 700 hPa was the main water vapor transportation channel in the snowfall area, and the abnormal water vapor flux center and the water vapor flux divergence center are the important reasons for the extremely strong snowfall. From the snowfall mechanism, January 3—4 big blizzard process belonged to the warm area cold flow snowfall, the atmosphere was in a moist symmetric unstable state, the blizzard region is located in the updraft near the sinking branch in the vertical superposition region with positive and negative spirals. And the high and low space jet coupled to form a vertical secondary circulation. The strong northwest airflow after the high trough was combined with the high efficiency of water vapor convergence transportation, the snowfall intensity was strong; However, January 24—28 was an atypical cold advective snowfall. Cold air moved southward in the lower layer, while dry cold air directly snowed due to the uplift of the bottom layer. The phenomenon of supersaturation is mainly in the lower layer, and the subcooling water is weak and lasts for a long time. Moreover, the occurrence and development of the low level jet stream in the two heavy snowfalls had a good correspondence with the positive vorticity advection around the high level jet stream, and the convergence strength corresponded to the snowfall intensity.

Key words: heavy snowfall, low level jet, helicity, vorticity advection, potential vorticity