Characteristics and formation mechanisms of the extreme rain，snow，and gale events in central and eastern China in April 2025

Based on conventional observations and ERA5 reanalysis data, this study analyzes an extreme weather event featuring widespread rain, snow, gales, and temperature drop across central-eastern China during 11—13 April 2025. The cold front passage triggered gales that spread southward from Inner Mongolia to North China and rapidly extended to Jianghuai region, with peak wind speeds and the maximum temperature drop occurring in the afternoon. The southern branch of the jet stream coupled with the northern branch that was characterized by strong cyclonic curvature over the Mongolian plateau. These two stable, quasi-stationary jet branches formed a robust secondary circulation cell, which served as the core dynamic driver for the extreme gales. The northern branch of the jet stream facilitated the downward intrusion of the high-PV (potential vorticity) air to the mid-stratosphere along isentropic surfaces, further enhancing downward transport of kinetic and baroclinic energy. The Mongolian cyclone remained stationary over Northeast China, while the anticyclone over central Mongolia moved southward, leading to dramatic increases in horizontal pressure gradient and directly triggering and sustaining the gales. Within the boundary layer, turbulent activities were dominated by surface heating during the daytime. In the nighttime, the stable stratification inhibited downward transport, strengthening the low-level northerly jet and vertical wind shear. This promoted turbulent mixing via Kelvin-Helmholtz instability and thus sustained nocturnal gales. The phase shift in the North Atlantic Oscillation (NAO) from negative to positive during 7—11 April triggered more efficient Rossby wave energy propagation. The southern branch wave train propagated eastward along the jet axis, while the northern branch wave train extended via Iceland–the Barents Sea–Lake Baikal. The anomalous low over the Barents Sea, cooperating with the Siberian high, guided high-latitude cold air to move southward. On 12 April, the superposition of these two wave trains over North China provided the background energy for the maintenance of the upper-level cold vortex and jet stream. Furthermore, a rapidly moving low pressure system over the Barents Sea on the 8th induced significant reductions in near-surface temperature and humidity along with markedly increased wind speed. This led to a substantial increase in the sea-air temperature difference, accelerating sea ice formation and the release of strong upward sensible and latent heat fluxes. They constituted a positive feedback mechanism, driving the downstream propagation of Rossby wave energy.