Abstract: A heavy rainstorm and strong convective weather event occurred in Changsha on April 29, 2024, leading the city to experience 'nightfall in one second' at noon. By using the multi-source observational data from wind profile radar, laser raindrop spectrum, doppler dual-polarization weather radar, and lightning locator, the evolution characteristics of small and medium-scale processes during the most extreme stage of the event are preliminarily analyzed. The results are as follows. (1) Changsha is a concentrated area of heavy precipitation, and strong lightning and thunderstorm winds. The maximum minute precipitation intensity at 13 stations reached 5 mm, and the maximum minute precipitation intensity at Lianhua National Station in Changsha exceeded the maximum minute rainfall during the "21.7" Henan heavy rainstorm. (2) The variation of the number concentrations of raindrops corresponding to different diameters with time is basically consistent with the time evolution of the minute precipitation of the raindrop spectrum, and the raindrops with a diameter of more than 1 mm contribute more significantly to precipitation. A high concentration of small-sized and medium-sized raindrops and a certain proportion of larger raindrops can lead to efficient heavy precipitation to a certain extent. The average spectrum of different precipitation types exhibited unimodal distribution. The maximum diameter and the number concentration of raindrops corresponding to each particle size of convective cloud precipitation are significantly higher than those of stratiform cloud precipitation. And the particles of convective cloud precipitation are more active. The mass-weighted average diameter and generalized intercept parameter (D_m-log₁₀N_w) show "continental convection" characteristics, both of which are positively correlated with the precipitation intensity. (3) Multiple convective cells in the mesoscale convective system merge and enhance, with new cells continuously developed at the rear side. The severe convective weather in the Changsha urban area is caused by the transit of bow echo, and the station with minute rainfall reached 5 mm corresponds to a differential phase shift rate (K_DP) large value area of 3.1^o km⁻¹. High near-surface differential reflectance factor (Z_DR) values, strong K_DP values, and large correlation coefficients (CC) indicate that the flat big raindrops with extremely high number concentration fall to the ground, and the heavy precipitation drag effect leads to the occurrence of thunderstorm gale. (4) The negative flashes predominate over the positive flashes, and the area with a large flash rate corresponds to the rainstorm area. The peak of lightning is 10-20 minutes before the precipitation maxima. The dual-polarization parameters Z_DR>2 dB and K_DP>0.5 º·km⁻¹ can be used to serve as strong lightning warning, with a leading time of about 6-12 minutes.