Wiktionary
n. The act of firing munitions containing silver iodide at passing clouds to make them more likely to produce rain.
Wikipedia
Cloud seeding, a form of weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud. The usual intent is to increase precipitation (rain or snow), but hail and fog suppression are also widely practiced in airports.
Cloud seeding also occurs due to ice nucleators in nature, most of which are bacterial in origin.
Usage examples of "cloud seeding".
I got that job because Bernie had become a celebrity in the GE Research Laboratory, in association with Irving Langmuir and Vincent Schaefer, for experiments with cloud seeding, and because the company decided to have regular newspaper people handle its publicity.