"Seeding" winter storm clouds over mountains is well established and understood. Clouds form as moist air is lifted and cooled during its passage across mountain ranges. Left to nature, many clouds are highly inefficient precipitators, retaining more than 90 percent of their moisture. By cloud seeding, the precipitation efficiency can be greatly improved. Generally, silver iodide is used in ground generators to produce artificial ice nuclei that form ice crystals. Spreading the nuclei via aircraft is also common. These crystals attract moisture from the surrounding air forming droplets that grow large enough to fall to the ground as snow. Some projects using ground-based silver iodide generators to seed winter storms over mountain areas in the western United States have operated continuously since 1950.
Cloud usually consists of very small droplets of water which cannot fall appreciably below the cloud base without evaporating. In this condition clouds are stable. Rain drops are about a million times heavier than cloud drops and rain develops only if the cloud droplets grow by some mechanism. Cloud seeding mechanism depends on the difference in vapour pressure over ice and super-cooled water at the same temperature. If ice crystals form in a super-cooled cloud, water evaporates of the droplets and migrates to the ice crystal, which grows and begins to fall increasing their growth rate by coalescence with other droplets and eventually melting and falling as rain drops.Vincent Schaefer (1906-1993) discovered the principle of cloud seeding in July 1946. Along with his associate Langmuir, he created a way of experimenting with super-cooled clouds using a deep freeze unit of potential agents (salt, talcum powder, soils, dust and various chemical agents) to stimulate ice crystal growth. The experiment was easily replicated and he explored the temperature gradient to establish the -40°C limit for liquid water. Within the month, Schaefer’s colleague, atmospheric scientist Dr Bernard Vonnegut is credited with discovering another method for “seeding” super-cooled cloud water. Dry ice and silver iodide agents are effective in changing the physical chemistry of super-cooled clouds, thus useful in augmentation of winter snowfall over mountains and under certain conditions and lightning and hail suppression. Minute crystals of silver iodide produced in the form of smoke acts as efficient ice forming nuclei at temperatures below -5°C to produce enormous number of nuclei (1015 per gram of silver iodide). When this smoke is introduced into super-cooled cloud, some ice crystals appear when temperatures fall below -4°C, but its formation rapidly increases with decreasing temperatures. Cloud seeding by silver iodide is done either from ground generators or from airborne generators. Substances other than silver iodide as artificial nuclei are lead iodide, cupric sulphide, cupric oxide, ammonium fluoride, cadmium iodide and iodine. However, all these are not as effective as silver iodide.
Although nobody with any real credibility claims that cloud seeding works, that has not stopped many from trying. In central Texas, they have been trying for more than 120 years. During an intense drought in the early 1890s, interest in rainmaking around San Antonio was high (San Antonio Daily Light, 1892). Rainmaking practitioners had developed secret concoctions and were using artillery, ballons, kites, and towers to blast or expel particles and gaseous emissions into the heavens. In 1891, the San Antonio Board of Trade appointed a committee to look into the possibility of bringing a rainmaker to south Texas and to inquire as to how many 8-inch mortar guns were on hand at the Rock Island Arsenal in Illinois. In April of 1892, committee chairman W. A. Bowen reported there were six, and several railroads said they would cheerfully render full transportation free of charge. But he also recommended the use of balloons instead of mortars. He called on several gentlemen under the charge of noted rainmaker General Robert G. Dyrenforth to meet with the Board and discuss arrangements using that method (The Daily Light, 1892). On November 14, 1892, the Board was pleased to receive and make welcome Messrs. John H. King and John H. Dickinson, who gave an account of their experiments under General Dyrenforth. They advised the Board it was not necessary to discuss the importance of this work, because if rain can be produced at will, land values will be raised by 300 percent. They told how they had received an appropriation from Congress and had been conducting experiments in South Dakota, but "the government was too slow, and the western people had become interested, so they were here, with their balloons, power, and other apparatus in Galveston ready to be sent, and now they wanted the citizens of San Antonio to come to the front and help by a kind word and a small subscription." The Board passed a resolution heartily recommending their work to the citizens of San Antonio.
To sum up, the really bad part is you’re putting cities and states in Jeopardy, just because you want to squeeze out a little extra precipitation. You’re really only doing it for your benefit, and that’s just ignorant. According to daily titian, when china hosted the summer Olympics, cloud seeding was used in neighboring areas of Beijing to guarantee clear skies over the game. After china saw that it was successful, china launched a full biological assault on the skies. Following the games, china officials admitted that the weather was out of their control and attributed to a 2009 blizzard to their own handy work. This shows that we’re not ready for cloud seeding or any other kind of weather modification. This also is an example of how cloud seeding has long-term effects.
"Rainmaking experiments: progress for the arrangements of carrying on operations", San Antonio Daily-News, April 29, 1892.
"The rainmakers: an important meeting held and arrangements made to experiment", San Antonio Daily Light, November 14, 1892.
"The rainmakers welcomed", The Daily Light, November 15, 1892.