Natural rainfall works much the same way. Ice crystals are formed when cold water contacts particles of dust, salt, or sand. The ice crystals provide a nucleus around which water droplets can attach, increasing the size of the droplet. When the droplet becomes large enough, it falls as rain. Cloud seeding is thought to increase the number of these nuclei available to take greater advantage of the moisture in the cloud and form raindrops that otherwise would not have formed.
Small droplets collide and coalesce until they form a drop large enough to fall.
George Bomar, meteorologist for the Texas Natural Resources Conservation Commission, and State Senator Jeff Wentworth visited a number of South Texas government agencies in 1996 and encouraged them to consider cloud seeding programs as a component of long term water management strategies. Bomar indicated state studies suggest cloud-seeding can increase the amount of rain by as much as 2.5 times. After the 1996 visits by Bomar and Wentworth, several agencies moved quickly to form the South Texas Weather Modification Association and initiate cloud seeding in May 1997. The Evergreen Underground Water District and the counties of Wilson, Karnes, Frio, Atascosa, McMullen, Live Oak, and Bee agreed to share the cost of a three-year program. While cloud-seeding does work, it is not cheap.