Abstract:
On 4 April 2018, a snowstorm accompanied by elevated thunderstorms occurred in North China. Using observations data from national and regional stations, as well as ERA5 reanalysis data, weather diagnosis and absolute momentum anomaly adjustment methods were employed to investigate the environmental conditions and thunderstorm triggering mechanisms of this weather event. The study found that: (1) This weather event occurred within the cold sector to the north of a passing cold front, representing an elevated thunderstorm event accompanied by a snowstorm under the influence of a return flow pattern during the cold season in North China. (2) Favorable environmental conditions for this event included the formation of a dry and cold air mass after eastern-route cold air encountered the blockage of the Taihang Mountains, leading to the emergence of a strong inversion layer that weakened the drag effect and thereby favored the development of convective activities. Meanwhile, horizontal water vapor transport in the middle troposphere provided necessary water vapor and energy support for the elevated thunderstorm. (3) Wet potential vorticity analysis indicated that the elevated thunderstorm occurred within a region of convective stability but symmetrical instability above the inversion layer, which was conducive to the development of tilted upward air currents. (4) Factors such as surface convergence lines and terrain induced initial upward motion. Although the neutral stratification suppressed upward motion, the upward air currents entered the region of symmetrical instability under the adjustment of absolute momentum anomalies (
ΔM adjustment), releasing energy and triggering sustained tilted upward air currents that extended to an altitude of 200 hPa, forming an elevated thunderstorm in early spring.