Dry weather causes a temperature increase in the clouds which in turn causes light raindrops. Very light raindrops cannot fall to Earth as rain. Silver iodine or dry ice is seeded onto the clouds to lower their temperature. Ice crystals then form and gradually increase in size. Due to the gravitational pull, these ice crystals fall to the Earth and transform into drops of water when melted by Earth’s warmer temperature. The rain helps wash the haze down to the Earth.