What Is Cloud Seeding? A Complete Guide to Weather Modification in 2026

What Is Cloud Seeding?

Cloud seeding is a form of weather modification technology that aims to change the amount or type of precipitation that falls from clouds. The practice involves dispersing substances — most commonly silver iodide (AgI), potassium iodide, or dry ice — into clouds to serve as cloud condensation nuclei or ice nuclei. These particles encourage water droplets or ice crystals to form, theoretically increasing rainfall or snowfall in targeted areas.

First demonstrated in 1946 by chemists Vincent Schaefer and Bernard Vonnegut at General Electric's research laboratory, cloud seeding has grown from a laboratory curiosity into a global industry. Today, more than 50 countries practice some form of weather modification, with the United States being one of the most active.

How Does Cloud Seeding Work?

The science behind cloud seeding relies on fundamental atmospheric physics. Clouds form when water vapor in the atmosphere condenses onto tiny particles called condensation nuclei. In nature, these nuclei include dust, pollen, sea salt, and other aerosols.

Cloud seeding introduces additional nuclei into clouds through two primary methods:

Glaciogenic Seeding

The most common approach targets cold clouds containing supercooled water — liquid water that exists at temperatures below freezing. Silver iodide is the preferred agent because its crystalline structure is nearly identical to that of natural ice. When silver iodide particles are introduced into a supercooled cloud, they serve as templates for ice crystal formation through a process called the Bergeron process.

As ice crystals grow at the expense of surrounding water droplets (because the saturation vapor pressure over ice is lower than over liquid water), they eventually become heavy enough to fall as precipitation — either as snow or, if they melt during descent, as rain.

Hygroscopic Seeding

Used primarily in warmer climates where clouds don't contain supercooled water, hygroscopic seeding disperses large salt particles (sodium chloride or calcium chloride) into the base of warm clouds. These particles are extremely effective at attracting water vapor, growing into large droplets that collide with and absorb smaller droplets — a process called collision-coalescence — until they're heavy enough to fall as rain.

Where Is Cloud Seeding Happening in the United States?

As of 2026, active cloud seeding programs operate in approximately 12 US states, with the majority concentrated in the western United States where water scarcity drives demand. The largest programs include:

• Idaho: One of the most extensive programs, spending approximately $4 million annually on snowpack enhancement in the upper Snake River basin
• Utah: Operates winter cloud seeding programs across multiple mountain ranges to boost reservoir levels
• Wyoming: The Wyoming Weather Modification Pilot Project has been studied extensively for its effects on snowfall in the Wind River and Sierra Madre ranges
• Colorado: Multiple programs targeting the Colorado River basin, critical for downstream water supply to seven states
• California: Programs in the Sierra Nevada and Central Valley, particularly during drought conditions
• Texas: Primarily focused on rain enhancement in agricultural regions and hail suppression

Meanwhile, a growing number of states have moved to ban cloud seeding entirely. Florida, Tennessee, Louisiana, and Montana have enacted prohibitions, and at least seven additional states have proposed similar legislation.

What Chemicals Are Used?

The primary chemicals used in cloud seeding operations include:

Silver Iodide (AgI): The most widely used glaciogenic seeding agent. A single ground-based generator can release billions of nanoscale particles over several hours. While proponents argue the amounts are too small to cause environmental harm, decades of cumulative use in the same watersheds has raised concerns about silver accumulation in soil and water.

Dry Ice (Solid CO₂): The original cloud seeding agent, used in Schaefer's 1946 experiments. At -78.5°C, dry ice causes extreme local cooling that triggers spontaneous ice crystal formation. Less common today due to logistical challenges.

Potassium Iodide (KI): Often combined with silver iodide in acetone solutions burned in ground-based generators.

Sodium Chloride (NaCl) and Calcium Chloride (CaCl₂): Hygroscopic agents used for warm-cloud seeding, particularly in tropical and Middle Eastern programs.

The Controversy: Does It Actually Work?

This is perhaps the most debated question in atmospheric science. After nearly 80 years of practice, the scientific evidence remains remarkably inconclusive.

Proponents, including the organizations that fund and operate seeding programs, typically claim 10-30% increases in precipitation over target areas. The most cited evidence comes from studies like the Wyoming Weather Modification Pilot Project, which reported an estimated 5-15% increase in snowfall, and the Idaho Power cloud seeding program, which has published analyses suggesting meaningful snowpack increases.

However, critics point to fundamental challenges in proving effectiveness:

• The attribution problem: How do you know it would not have snowed or rained anyway? Weather is inherently variable, and isolating the effect of seeding from natural variation requires extraordinarily long study periods.

• Publication bias: Programs funded by water utilities or state agencies have a financial incentive to report positive results.

• Lack of controlled experiments: True randomized controlled trials of cloud seeding are rare, expensive, and difficult to design.

The National Academy of Sciences has repeatedly called for more rigorous evaluation, noting in multiple reports that "there is no convincing scientific proof of the efficacy of intentional weather modification efforts."

Environmental and Health Concerns

The environmental implications of cloud seeding extend beyond the question of whether it works:

Silver contamination: Studies have found elevated silver concentrations in soil and waterways near long-running seeding programs. While individual events release small quantities, cumulative deposition over decades is a legitimate concern for aquatic ecosystems.

Precipitation redistribution: Cloud seeding does not create new water — it redistributes existing atmospheric moisture. If seeding causes rain to fall over one area, that moisture may no longer be available for natural precipitation elsewhere, potentially creating winners and losers.

Ecosystem disruption: Altering natural precipitation patterns can affect plant communities, wildlife habitats, stream flows, and groundwater recharge in ways that are difficult to predict or monitor.

Informed consent: Perhaps the most fundamental concern is that cloud seeding affects everyone under the treated clouds — including those who never consented to having their atmosphere modified. This raises profound questions about individual rights and democratic governance.

How to Track Cloud Seeding Operations

ChemTrail.app uses publicly available ADS-B (Automatic Dependent Surveillance-Broadcast) data to track known cloud seeding aircraft in real-time. By monitoring the transponder signals of aircraft registered to cloud seeding operators, the public can see when and where seeding operations are occurring.

You can explore our live flight tracker, browse the aircraft database, or check cloud seeding status by state to learn what's happening in your area.