Next section The Science of Cloud Seeding Figure 1 . The target area is the oblong shape that stretches from Big Spring to Roscoe to Lamesa. The percent increase in rainfall is indicated by the bar at the left. To understand cloud seeding, you first have to know some basic facts about the weather.
All air contains moisture.
When warm air rises from the Earth's surface and begins to cool, some of the moisture condenses into tiny droplets that cause clouds. Before these tiny droplets can form raindrops or hailstones, they have to merge with millions of others before they are heavy enough to fall to the ground. For precipitation to form, temperatures inside the cloud have to be less than the freezing point of water. When droplets of this supercooled water encounter specks of dust, salt, or sand they form small ice crystals. Water vapor in the cloud then freezes directly onto the surface of these crystals and they gain weight and fall.