From the Weather Center
by John Simon
Cloud seeding is a weather modification technique that improves the cloud to produce rain or snow by adding condensation nuclei to the sky for the snowflakes or raindrops to form.
Cloud seeding is used all over the world for enhancing snowfall and increasing mountain snowpack and supplementing the natural water supply available to the communities of the surrounding areas. Cloud seeding also halts thunderstorms by utilizing dry ice to change the thunder cloud to a snow cloud. Cloud seeding might also reduce lightning intensity and frequency.
Cloud seeding can be done by either ground based generators or aircraft such as small planes, rain rockets, or drones. Weather modification drones are more efficient and flexible, with longer endurance and lower costs. In one region of China, which has become a leader in cloud seeding technology, weather modification operations are expected to increase annual rainfall by 15 per cent.
Most cloud seeding operations use a compound called silver iodide (AgI) to aid in the formation of ice crystals. Silver iodide exists naturally in the environment at low concentrations, and is not known to be harmful to humans or wildlife. Silver iodide acts as a condensation nuclei to aid in the formation of snowflakes.
During dry winters, when storm systems are absent for long periods, cloud seeding cannot occur, because it requires the presence of moisture filed clouds to be successful.
In the 1940s, some summer cloud seeding projects seeking to end drought like conditions in New York City angered officials in the Catskills who feel that such efforts were harmful to their tourism industry.