Dr. Vincent Schaefer undertook the first weather modification experiments for General Electric in 1946. Cloud seeding companies use aircraft or ground generators to release silver iodide particles into clouds when temperature and moisture are ripe for rain. Attracting clumps of moisture, the silver iodide particles trigger formation of ice crystals which then fall as additional rain or snow.Cloud seeding requires that cloud contain enough moisture for the silver iodide crystals to tip near-saturation into rain or snow.