>Each of the cloud seeding projects uses specially-equipped aircraft designed to place seeding materials (in the form of pyrotechnic devices, or flares, containing silver iodide and other compounds) into convective towers (turrets of growing thunderstorms) to induce them to expand and process more atmospheric water. The seeding is achieved by burning flares either mounted on the wings of single and twin-engine aircraft or held in racks, and dropped (ejected), from the underside of the aircraft fuselage.

https://www.tdlr.texas.gov/weather/summary.htm