Characteristics and causative analysis of extreme rain, snow and gale weather events in central and eastern China during April 2025

Based on conventional observations and ERA-5 reanalysis data, this study analyzes an extreme weather event featuring widespread rain-snow, gales, and temperature drops across central-eastern China during 11-13 April 2025. The cold front passage triggered gales expanding southward from Inner Mongolia to North China and rapidly extending to Jianghuai region, reaching peak wind speeds and the maximum temperature drop in the afternoon. The southern branch jet stream coupled with the northern branch jet stream characterized by strong cyclonic curvature over the Mongolian Plateau. These two stable, quasi-stationary jet branches formed a robust secondary circulation cell, constituting the core dynamic mechanism for these extreme gales. The northern branch jet stream facilitated the downward intrusion of high-PV air to the mid-stratosphere along isentropic surfaces, further enhancing the downward transport of kinetic and baroclinic energy. The Mongolian cyclone stalled over Northeast China, while the anticyclone over central Mongolia moved southward, causing a dramatic increase in the horizontal pressure gradient, representing the direct cause for the initiation and maintenance of the gales. Within the boundary layer, turbulent activity was dominated by surface heating during the day. At night, stable stratification inhibited downward transport, strengthening the low-level northerly jet and vertical wind shear. This promoted turbulent mixing via Kelvin-Helmholtz instability, sustaining nocturnal gales. A phase shift in the North Atlantic Oscillation (NAO) from negative to positive between 7 and 11 April triggered more efficient Rossby wave energy dispersion. 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. An anomalous low over the Barents Sea, cooperating with the Siberian High, guided high-latitude cold air southward. On 12 April, the superposition of these two wave trains over North China provided 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 speeds. 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. This constituted a positive feedback mechanism, driving the downstream propagation of Rossby wave energy.