Destructive misinformation-mongers at work: What is cloud seeding? And what’s really fueling California’s heavy rain
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Brandi D. Addison USA TODAY NETWORK Dec. 23, 2025, 11:14 a.m. PT
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* Heavy rain from an atmospheric river is causing flooding and road closures across California. * Social media posts have incorrectly blamed weather modification, like cloud seeding, for the severe storms. * California's rain is caused by a natural atmospheric river pattern, not cloud seeding. * Cloud seeding is a limited practice in California used to slightly increase precipitation, not create major storms.
Emergency crews have carried out swift-water rescues in multiple regions after creeks and urban drainage systems overflowed. At the same time, saturated hillsides raised concerns about landslides and debris flows, especially near recent wildfire burn scars. Forecasters warn impacts may continue as additional rounds of rain and mountain snow move in through early January.
And when extreme events stack up — blizzards in one region, back-to-back flooding in another — speculation often follows. Social media posts have revived claims that cloud seeding or other forms of weather modification are behind some of the most significant flood events in the U.S. this year, including the Fourth of July floods in Texas.
But the reason is as simple as it gets: the weather.
What is weather modification? How does cloud seeding work?
Weather modification is "any activity performed with the intention of producing artificial changes in the composition, behavior, or dynamics of the atmosphere," according to the National Oceanic and Atmospheric Administration.
Cloud seeding is a type of weather modification developed in the 1940s to increase rainfall or snowfall, particularly in drought-prone or dry regions. It involves injecting a small amount of a chemical — usually silver iodide — into existing clouds to encourage the formation of larger water droplets or ice crystals, according to the National Oceanic and Atmospheric Administration.
Most occurs because most clouds carry moisture but don’t produce rain or snow because their droplets or crystals are too small to fall. Silver iodide acts as a “cloud condensation nucleus,” allowing water vapor to gather into heavier droplets or crystals that gravity can pull to the ground.
Once a cloud is seeded, it releases its moisture relatively quickly and does not continue producing rain beyond that initial burst. The impact ends when the cloud has rained itself out.
Cloud seeding is never permitted in storms that have the potential to produce severe weather, such as tornadoes or flash floods.
Does cloud seeding happen in California?
California has used cloud seeding for several decades, but on a limited, regulated, and highly localized basis, primarily to support water supplies. It is not used to create storms, control weather systems, or cause flooding.
Cloud seeding in California is typically carried out by local water agencies, irrigation districts, or utility authorities, most often in parts of the Sierra Nevada and select Southern California watersheds. The goal is to enhance snowfall during existing winter storms slightly, helping boost snowpack that later feeds rivers and reservoirs.
For example, from late 2023 into early 2024, the Santa Ana Watershed Project Authority (SAWPA) operated a multi-year cloud-seeding pilot program aimed at modestly increasing precipitation during storms to support regional water supplies. The program relied on ground-based silver iodide generators targeting specific mountain areas and worked only when suitable storm conditions were already present.
However, in July 2025, SAWPA announced in a release that the pilot program was being discontinued after early data showed insufficient evidence that cloud seeding significantly increased rainfall or snowpack.
Agency officials said the results did not demonstrate a strong enough benefit to justify continuing the effort. Officials also noted that wildfire burn scars from the 2024 fire season within the watershed raised concerns about debris flows if precipitation were increased, prompting additional caution and contributing to limits on operations.
Where is the rain coming from?
California’s heavy rain is not the result of cloud seeding. Instead, it’s being driven by a long-duration atmospheric river pattern repeatedly directing Pacific moisture at the West Coast, according to the Climate Prediction Center.
A ridge of high pressure over the Bering Sea paired with a trough in the northeast Pacific is acting like a conveyor belt, steering storm after storm into California and the broader West. Atmospheric rivers — long, narrow plumes of moisture — are arriving in succession, leaving little time for rivers, soil and infrastructure to recover between systems.
"A Bering Sea ridge and northeast Pacific trough will keep atmospheric rivers aimed at the western U.S.," the Climate Prediction Center wrote. "During the busy holiday travel period and beyond, impacts may include flooding, landslides, and difficult mountain travel. Burn scar areas could see flash flooding and debris flows, and power outages are possible due to strong winds and heavy precipitation."
Forecasters say this pattern is expected to persist through the end of December and into early January, increasing the risk of cumulative flooding impacts across already saturated areas.
Southern California is naturally experiencing one of its rainiest months of the year, which amplifies flooding risks. Meteorologists also point to La Nin~a, a climate pattern that can shift the jet stream and influence storm tracks, potentially contributing to the unusually persistent rainfall in the region.
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