Synoptic diagnosis and comparative analysis of multi-source observational characteristics of an elevated thunderstorm accompanied by heavy snow in Henan

To improve the understanding of the mechanisms of elevated thunderstorms accompanied by heavy snow in Henan Province and the capability of applying multi-source data, an elevated thunderstorm with heavy snow that occurred in Henan in December 2023 is analyzed. Conventional observations and ERA5 reanalysis data are used to examine the weather conditions, circulation background, and environmental conditions of the event. Synoptic diagnosis is then performed on the moisture, dynamic, and instability mechanisms. Multi-source observations are further employed to analyze the observational characteristics of the event. The results are as follows. (1) The event occurred as a 500 hPa transverse trough moved southward and a southern branch trough shifted eastward. A strong 700 hPa southwesterly jet overrode the deep cold dome formed by near-surface easterly cold air, creating a baroclinic structure. The dense lightning area and the heavy snow zone were located about 400 km behind the surface cold front. (2) High specific humidity and strong moisture convergence in the middle and upper troposphere provided an abundant moisture supply. Low-level frontogenesis and its secondary circulation played an important dynamic role. The ascending branch of the frontogenetic circulation, together with the lifting of the mid- and upper-level southwesterly jet, generated strong upward motion. Conditional instability above the frontal zone provided the initial energy, while conditional symmetric instability near the low-level front sustained the subsequent development of the event. (3) Observations from a microwave radiometer and a wind profiler verified the diagnosed environmental, moisture, and dynamic conditions. The persistent thickening of the low-level cold dome, the mid-level warming, and the sharp increases in water vapor density and liquid water content in the lower and middle levels were associated with the maintenance of the inversion-cold dome structure and the moisture transport near 700 hPa. The strengthening of the low-level northeasterly winds and the mid-level southwesterly jet, together with the development of vertical wind shear in the lower and middle troposphere, favored the development of this cold-season elevated thunderstorm and the heavy snowfall. (4) Satellite and dual-polarization radar observations further confirmed the diagnosed instability mechanisms and dynamic effects. The brightness temperature of the cold cloud cores remained between -50~-30 ℃, and the reflectivity factors of the convective cells reached 45~50 dBz, which was consistent with the establishment of conditional instability. The banded echoes above 30 dBz, together with the "S"-shaped zero velocity line and "bull's-eye" pattern in the low- and mid-level radial velocity, reflected the presence of conditional symmetric instability. The strong echoes above 40 dBz extended above the melting level. Above the melting level, high correlation coefficient values and the vertical extension of differential reflectivity columns and specific differential phase columns also indicated the strong upward motion.