Weather modification is usually related to the so called cloud seeding which includes spraying different substances, such as silver iodide, salts and dry ice, to allow for formation of larger rain drops and precipitations and for removal of mist and clouds.
Hail protection is based on the technology of introducing an ice-forming reagent into the hail-bearing cloud at the moment before formation of hail grains. Its particles play the role of cores which take away the overcooled water from the cloud and do not allow for excessive growing of the natural ice cores. Thus, more hail grains are formed having smaller sizes. They melt during their falling down or cause less damage in case they have not melted completely. It is important to note that the strong vertical air streams continuously supply the cloud with overcooled water and ice crystals, therefore, new amounts of reagent have to be introduced at definite time intervals until the hail-hazard passes away. Silver iodide (AgI) is used currently as an ice-forming reagent, and lead iodide (PbI) was used as such in the past.
Three methods for seeding clouds with an ice-forming reagent are used: by means of terrestrial generators, airplanes and anti-hail rockets.