Why cloud seed?  

Much of the Western United States relies on the water that melts out of Rocky Mountain snowpack into the Colorado River and its tributaries. Cloud seeding is the only way to increase snowfall and in turn, increase water supplies in the arid West. The Colorado River Basin is experiencing long-term drought driven by rising temperatures, which is drying up the water supply that more than 40 million people rely on as drinking water for communities, to power economies and to sustain habitat for plants and animals.  

Cloud seeding allows water managers to boost the amount of snow that falls from certain storms. Cloud seeding can increase a storm’s snowfall by up to 15% and associated stream flows up to 5%. This added snow could equal up to 80,000 acre-feet of water annually once it melts, which is about enough water to serve about 160,000 households on average per year. While the Colorado River District’s primary goal in participating in cloud seeding is to increase our water supply, cloud seeding has secondary benefits: improving snow conditions for winter recreation, such as skiing, snowboarding and snowmobiling, and improving runoff conditions that benefit summer recreation such as rafting and fishing.  



The Colorado River District manages the Central Colorado Mountain River Basin cloud seeding program, which operates along the northern and central Rocky Mountains of Colorado.  In total, the Colorado River District manages 24 cloud-seeding generators which seed clouds over portions of Eagle, Grand, Pitkin and Summit counties. Our partners make this possible with funding and technical support. Partners include member agencies of the Front Range Water Council, the Colorado Water Conservation Board, ski areas and water utilities in Arizona, southern California and Nevada.  

How it works  

Precipitation forms when water droplets in clouds condense on a nucleus made up of tiny particles of dust, salt or smoke, when enough water condenses onto a nucleus, the water becomes heavy enough to fall to the ground as rain, snow, sleet or hail. To put it simply, the practice of cloud seeding sends tiny particles into clouds to serve as the nucleus. Then, water condenses around the nucleus and falls to the ground as snow.  

In the Central Colorado Mountain River Basin cloud seeding program, a small amount of silver iodide particles are sprayed across a flame emitted from a propane generator. These particles rise into the clouds. The silver iodide particles cause moisture in the cloud to freeze and create ice crystals at a warmer temperature, thereby creating more snow. As more and more water freezes around the particles, the water falls to the ground as snow.  

Cloud seeding is most successful in specific conditions, and managers do not seed every storm. Water managers focus on storms carrying a lot of moisture. Air temperatures, wind and height of the clouds are all factored into the decision-making process to determine if a storm will be seeded.  

Silver iodide is a naturally occurring substance. It has no known immediate or longterm environmental impacts. It also has a hexagonal, crystal shape making it particularly conducive for forming snowflakes.  

Studies [LINK OR FOOTNOTE NEED TO LOOK AT CITATIONS W DK] indicate there is little evidence cloud seeding to increase rainfall in one area deprives another area of normal rainfall. There is evidence that the practice actually increases precipitation downwind of where storms are seeded, as seeded clouds continue moving.  



Wyoming Weather Modification Pilot Project (Medicine Bow/Sierra Madre)  

Statistical, physical, trace chemical and modeling evidence –  

SNOWIE – Idaho Power Company and National Science Foundation – Robust field campaign that is first “visual proof of seeding” or mapped plumes  

Gornbein 2010 Southern California Edison (Sierra Nevada) – Manton et al. 2011, Snowy Precipitation Enhancement Research Project (Snowy Mountains, Australia) – Statistical and trace chemical evidence