From 19 to 20 February 2024, precipitation caused by elevated convection occurred in Shandong peninsula for two consecutive days, but there were significant differences in phases (heavy snowfall on the 19 February 2024 and freezing rain on the 20 February 2024). In this paper, utilizing multisource meteorological data from conventional meteorological observation, three-dimensional lightning locator, dual polarization radar and ERA5 reanalysis, the differences of their thermodynamic mechanism were compared and their conceptual models were proposed. The results shows: (1) The precipitation on the 19 and 20 February 2024 occurred under the background of similar circulation: That is, there was a deeply sphenoid cold air pad above the ground with a temperature below 0℃, forming a low-level strong inversion layer. The climb of the southwest jet along the cold air pad in front of the southern trough over 700 hPa not only provides abundant water and dynamic conditions, but also its intensity change is an important factor of formatting melt layer. (2) There are a variety of instability mechanisms in this process: In the lower layer, there is a conditional symmetrical instability zone near the interface between cold and warm air, and the warm and humid airflow rises obliquely on the cold pad, and in the middle layer, above the symmetrical instability zone, with the southwestern jet pushing northward twice, the conditional instability zone is established near 500 hPa, and the tilted rising flow into this area triggers elevation convection. The vertical circulation caused by local dynamic frontogenesis is also an important influencing mechanism of the extreme disaster weather by elevated convection. (3) The blizzard on 19 February 2024 was caused by frontogenesis dynamic process, and the blizzard belt was parallel with the frontogenesis belt. On the 20 February 2024, the warm advection caused the front dissipation near 700 hPa, and the frontogenesis of the warm front in the lower layer, which not only caused the cold pad to gradually become thinner, but also formed a thicker melting layer, so most of the hydrometeors melted into raindrops, forming freezing rain. The distribution is closely related to the low-level warm front: The freezing rain is near the warm frontogenesis, the snowfall zone distributes more northern, and the ice particle belt is between them. (4) The differences in precipitation phases are caused by both differences in environmental fields and differences in cloud microphysical structures. The microphysical characteristics of precipitation particles in clouds, the liquid water content in the melting layer, and the thickness, strength, and duration of the melting and freezing layers all have significant impacts on the precipitation phase. On the 19 February 2024, the convection developed higher, and the 30 dBz extended to the height above −20—−10°C, and multiple snowfall clouds continuously act with high snowfall efficiency. During heavy snowfall, the polarization features of radar observation indicate that Z_DR is −1—0.5 dB, CC＞0.98, and K_DP does not exceed 1°/km, showing the characteristics of uniform heavy snowfall. There was a significant melting layer bright band in radar reflectivity during freezing rain on the 20 February 2024, and the CC was less than 0.9 (0.7—0.9) and the gradient was larger, while the Z_DR below this height increased to 1—3 dB, corresponding to water droplets or ice particles with larger particle size.

Intense observations of precipitation around the Mount Tai during an extreme heavy rain event in autumn 2022 in Shandong province by regional automatic weather stations, radars, wind profilers and satellites are analyzed and possible reasons for the precipitation distribution are explored. The results are as follows: (1) The heavy rain event in Shandong occurred under the background of strong southerly flow in the middle and lower troposphere, and the period of heavy rainfall was concentrated from 23:00 BT 1 October to 02:00 BT the next day. The 100 mm rainfall contour showed a "reverse bow" shape, stretching across the north and west sides of the Mount Tai, with over 170 mm of precipitation at each center. In contrast, rainfall on the south side of the Mount Tai was significantly weaker. (2) Heavy rain belts corresponded to the convergence line-mesoscale vortex system on the ground. The mesoscale vortex on the west side of the Mount Tai formed due to the encounter of the cold flow around the north side of the mountain and the warm flow around the south side. It resulted in a strong precipitation center with single-peak precipitation on the west side of the Mount Tai. The convergence line on the north side of the mountain was sustained and rebuilt, resulting in longer precipitation time and greater accumulated precipitation on the north side of Mount Tai. Hourly precipitation on the north side exhibited a double peak pattern. (3) The two precipitation peaks observed on the north side of the Mount Tai corresponded to the two parallel echo bands of radar reflectivity. The first echo band was located on the north slope of the Mount Tai and remained quasi-stationary for a long time, which corresponded to the ascending branch of the horizontal vorticity circulation on the north side of the Mount Tai. Its formation mechanism is the strong development and maintenance of horizontal vorticity due to the southwesterly low-level jet with strong vertical shear and the northeasterly airflow obstructed by the mountain at low levels in nighttime. The second precipitation echo band corresponded to a cold front cloud system. When it approached the north side of the Mount Tai, it was influenced by the leeward upslope southwesterly low-level airflow, resulting in an increase in the radar reflectivity factor. The corresponding ground wind field was featured by a reconstruction process of the convergence line. (4) On the west side of the Mount Tai, the ground convergence line moved southeastward under the drive of low-level cold air, causing the echo band to gradually evolve into a "reverse bow" shape and the heavy rain band also exhibited a "reverse bow" distribution. The south side of the Mount Tai is located under the subsidence branch of the horizontal vorticity formed by strong vertical shear low-level jet, where precipitation was significantly less compared to that in the north and west sides.

Based on multi-source observational data, the extreme convective gale caused by two different types of storms during a severe convective process in Huang-Huai region on 30 April 2021 is discussed. Results indicate that the severe convective process occurred under the background of the Northeast Cold Vortex with strong vertical wind shear and stratification instability. The initial convective activities were triggered by a surface cyclone and associated front and developed rapidly. The convective systems went through different evolution stages such as organization, movement, initiation and explosive development of isolated storm cells, and merge and reorganization in the subsequent 10 hours of propagation process, during which different characteristics of convective winds were caused by two different types of storms. Represented by Huai'an station, extreme convective winds (36.2 m/s) occurred in central Jiangsu due to the downburst caused by a strong supercell storm. An obvious hook echo structure occurred in the lower layer of the storm, corresponding to the deep mesocyclone with strong cyclonic rotation. As the extreme wind occurred, the mesocyclone stretched upward and downward simultaneously, accompanied by a horizontal rapid contraction process. The downdraft throughout the whole storm was located at the back of the hook structure of the storm, and the strong downdraft diverged outward rapidly near the ground, accompanied by a rapid drop of the strong reflectivity core in the storm. This resulted in extreme winds on small spatial-temporal scale and significantly discontinuous spatial distribution in Huai'an. Represented by Nantong area, the development of extreme winds in southeastern Jingsu involved interactions between multi-scale weather systems. An obvious gust front developed at the front of the linear convective system, resulting in large area of surface gales above Grade 10. The extreme gale in Tongzhou bay of Nantong (47.9 m/s) occurred at the back of the gust front, which was caused by the superposition effect of multi-scale systems, including the strong cold pool induced by the linear convective storm and the surface cold front, the rapid development of the surface cyclone that entered the sea and the downdraft in the rear of the storm with downward transfer of upper wind momentum.

This study examined the rainfall characteristics and related synoptic processes of two extreme rainfall events that affected North China during 29 July–1 August 2023 (“23·7” rainstorm) and 3–5 August 1996 (“96·8” rainstorm), respectively. A stable dual-typhoon circulation pattern was observed in both rainstorm events. The surviving vortex of a landed typhoon, slowly approaching the rainstorm region, was blocked by a high-pressure system as it moved northwestward. Meanwhile, the second typhoon over the western Pacific Ocean facilitated remote northward transport of moisture. The low-level jet between the surviving vortex and the western Pacific subtropical high relayed moist warm air from the area of the South China Sea and western Pacific into the rainstorm region. Although the circulation patterns are similar, the stratification conditions, driving factors, and moisture budget of the two rainstorms differed during the main period of rainfall. The “23·7” rainstorm was categorized as warm-sector rainfall, as a result of the lifting of warm moist air over the eastern foothills of Taihang Mountains. In comparison with the situation of the “96·8” rainstorm, the surviving vortex of the “23·7” rainstorm traveled further northeastward and directly impacted the occurrence and progression of the rainfall, leading to relative northward displacement of the rainfall center, while the stronger net inward moisture flux caused greater regional average rainfall. The “96·8” rainstorm was broadly analogous to precipitation of a cold front, and the rainfall center was observed in the convergence area of warm and cold air masses before the mountains; the surviving vortex did not exert direct impact on the rainfall; and the more unstable stratification led to stronger hourly rainfall. The results derived through comparison of the two rainstorms could serve as valuable scientific reference for operational forecasting of heavy rainfall under similar environmental conditions over North China.

North China experienced devastating rainfall from 29 July to 1 August 2023, which caused substantial flooding and damage. This study analyzed observations from surface rain gauges and S-band dual-polarization radars to reveal the following unique features of the precipitation evolution from the plain to the mountains during this event. (1) The total rainfall was found concentrated along the Taihang Mountains at elevations generally > 200 m, and its spatiotemporal evolution was closely associated with northward-moving low-level jets. (2) Storms propagated northwestward with southeasterly steering winds, producing continuous rainfall along the eastern slopes of the Taihang Mountains owing to mountain blocking, which resulted in the formation of local centers of precipitation maxima. However, most rainfall episodes with an extreme hourly rainfall rate (HRR), corresponding to large horizontal wind shear at low levels, actively occurred in the plain area to the east of the Taihang Mountains. (3) The western portion of the extreme heavy rain belt in the north was mainly caused by long-lasting cumulus–stratus mixed precipitation with HRR < 20 mm h⁻¹; the eastern portion was dominated by short-duration convective precipitation with HRR > 20 mm h⁻¹. The contributions of convective precipitation and cumulus–stratus mixed precipitation to the total rainfall of the southern and middle rain belts were broadly equivalent. (4) The local HRR maxima located at the transition zone from the plain to the mountains were induced by moderate storm-scale convective cells with active warm-rain processes and large number of small-sized rain droplets. (5) During the devastating rainfall event, it was observed that the rainfall peaked at around 1800 local time (LT) every day over the upstream plain area (no diurnal cycle of rainfall was observed in relation to the accumulated rainfall centers over mountain areas). This was attributable to convective activities along the storm propagation path, which was a result of the more unstable stratification with a suitable steering mechanism that was related to afternoon solar heating and enhanced water vapor. The findings of this study improve our understanding and knowledge of the extreme precipitation that can develop from the plain to the mountains in North China.