Cloud seeding is only effective when there are certain types of rain bearing clouds present. In the early days they used to tip bags of dry ice out the back of the plane into the cloud. The particles are intended to be a catalyst to form rain drops. These days they use silver iodide and fly under the clouds using an updraft to take it up into the cloud. They did quite a bit of cloud seeding over the catchment areas of Tasmania's dams trying to get more water for hydro electricity. I think the results were a bit hit and miss, I don't think they do it these days. It was always hard to convince governments to fund it.
