From The Independent:
Recently both Russia and China have claimed to be able to use cloud seeding to increase rainfall and snowfall, or change the location of where it falls. In the past, snow-making experiments have been carried out in North American ski resorts in the past with little evidence of success. So how have the Russian and Chinese scientists achieved this feat and what evidence is there that it is in fact due to cloud seeding?
The seeding method used is to add tiny particles of silver iodide to the clouds and there is solid science behind this method. At temperatures a few degrees below zero degrees centigrade, clouds consist mainly of supercooled water droplets. These clouds can be quite stable, but silver iodide has an ice-like structure and it will cause a few of these water droplets to freeze. Once you have ice particles mixed in with the supercooled droplets, these crystals grow rapidly to form snowflakes, causing the cloud to precipitate. The effect is that the water is released from the cloud.
[Read more at The Independent]