Observations of thunderstorms in New Mexico were made with a vertically-scanning, 3-cm radar on a mountain top. Prior to a cloud-to-ground lightning discharge nearby, the radar echo overhead was usually quite weak, indicating low intensities of precipitation there. Following the lightning it was observed sometimes that in the region of the cloud where the discharge occurred the radar echo intensity rapidly increased, and shortly thereafter a gush of rain or hail fell nearby. These studies confirm earlier radar observations, made by the authors at Grand Bahama Island, B.W.I., in which it was found that lightning is often followed in the cloud by a rapidly intensifying echo and then by a gush of rain at the ground. The increases in radar reflectivity in small volumes of the cloud following lightning suggest that the electric discharge is influencing the size of particles in the cloud. An analysis indicates that within 30 seconds after a lightning discharge, the mass of some droplets may increase as... Abstract Observations of thunderstorms in New Mexico were made with a vertically-scanning, 3-cm radar on a mountain top. Prior to a cloud-to-ground lightning discharge nearby, the radar echo overhead was usually quite weak, indicating low intensities of precipitation there. Following the lightning it was observed sometimes that in the region of the cloud where the discharge occurred the radar echo intensity rapidly increased, and shortly thereafter a gush of rain or hail fell nearby. These studies confirm earlier radar observations, made by the authors at Grand Bahama Island, B.W.I., in which it was found that lightning is often followed in the cloud by a rapidly intensifying echo and then by a gush of rain at the ground. The increases in radar reflectivity in small volumes of the cloud following lightning suggest that the electric discharge is influencing the size of particles in the cloud. An analysis indicates that within 30 seconds after a lightning discharge, the mass of some droplets may increase as...