Enhancing our water supply 

Cloud seeding takes place in Utah from the months of November and into April. It only occurs during snowfall events where atmospheric conditions (such as temperature and moisture) favor the enhancement of snow – never under clear conditions. 

How cloud seeding works

Utah uses both ground-based seeders and aircraft. In both seeding methods, silver iodide is dispensed into winter clouds to help form ice crystals. Ground-based seeders are placed along foothills and higher elevations, and the release of the silver iodide  is timed so that air currents carry them high into the cloud. Aircraft operate inside the cloud for more precise targeting.

This process is effective because clouds are formed by water vapor and airborne particles (cloud condensation nuclei). Under certain natural conditions, water droplets will freeze together around the particles and, when heavy enough, fall from the sky as snow. Often, the amount of water that can fall as snow is limited by the number of particles around which ice crystals can form. That is why adding particles, or seeds, facilitates and accelerates the process. This may lead to more snow falling than would have under natural conditions.

White lines in the sky? Not cloud seeding

Occasionally, we’re asked if the white lines people see in the blue sky are related to our operations. Cloud seeding happens within or above clouds that are already producing some amount of snowfall. Because silver iodide is released inside winter storm clouds, cloud seeding does not produce visible white lines in the sky. You can learn about contrails – or condensation trails – in this NASA publication, and here on the Weather Modification Association website.  

Why Utah cloud seeds

Since snowpack is Utah’s largest reservoir, increasing the amount of snow that falls is a win for the water supply. It doesn’t work just anywhere. The conditions have to be right. Luckily, Utah’s topography, climate and reservoirs make winter snowpack enhancement cost-effective. Statistical analysis shows an average increase in precipitation of 5-15% in seeded areas at a cost between $5-10 per acre-foot for the additional water. The field program is funded jointly by the state and local water interests. 

Cloud seeding can only occur when there is sufficient water in the atmosphere along with other meteorological parameters (i.e. during precipitation). It is a long-term water management strategy that enhances snowfall. See our FAQ sheet to learn more.