Abstract:

Using automatic weather stations, dual-polarization radar, wind profile radar and ERA5 reanalysis data, the causes of an extreme snowstorm and lightning weather event that occurred in He'nan province on March 16, 2023, were analyzed. The results showed that the main weather systems responsible for this extreme snowstorm process were the trough, shear line, jet stream, and Northeast Cold Vortex(NCV). The cold vortex, maintained stably with the -39 ℃ cold center, permitted cold air to persistently move southward at its rear, forming a deep cold cushion below 850 hPa. Meanwhile, southwest warm and moist airflows ascended along the cold cushion in the middle and upper levels, forming a typical "north-south type" snowfall weather pattern in He'nan province. The heavy snowfall area overlapped the northern region where the total precipitable water was 20 mm and the 700 hPa strong convergence center. The topographical uplift of the central and western regions of He'nan further facilitated this extreme snowfall event. The joint effect of cold advection and secondary circulation caused a sudden drop in local temperature, leading to an earlier-than-expected phase transition, resulting in multisite snowfall or snow depth exceeding historical records. The correlation coefficient product from the dual-polarization radar provided an important reference for monitoring phase transitions. Below 850 hPa, the air temperature was consistently below 0 ℃, and the 2-meter temperature dropped to around 1 ℃, serving as forecasting indicators for snowfall. Convergent shear and frontal secondary circulation were favorable for elevated thunderstorms, with the height of the 20 dBz echo exceeding -20 ℃ level can serve as a critical indicator for the occurrence of thunderstorms.

Key words: Snowfall forecast, Thunderstorms, Northeast Cold Vortex(NCV), Phase transition