Read Rainmaker's Peer-Reviewed Study in Atmosphere
Today, Rainmaker's research team published a peer-reviewed study of our past-season cloud seeding operations, validation methodologies, and results in the journal Atmosphere.
The study, Radar-Observed Cloud Seeding Signatures from UAS-Based Glaciogenic Seeding: The 2025–2026 Rainmaker Season, analyzes 71 radar-observed seeding signatures from 15 intensive observing periods (IOPs) and asks whether uncrewed aircraft system (UAS) silver iodide flare releases produce attributable radar signatures; how consistently they behave across a season; and how much radar-estimated precipitation is associated with them.
Independent scientists reviewed our study prior to publication. This marks an important step forward for Rainmaker as a scientific research organization and for the weather modification industry as a whole.
Background
Rainmaker uses cloud seeding technology to increase the amount of precipitation falling into a target area. Two critical parts of our platform are validation (how we prove we generated new precipitation) and QPE (how we quantify that new precipitation).
Step 1: Validation
Rainmaker’s scientists review radar data at the end of each IOP. They look for regions of enhanced reflectivity which (a) are clearly distinguishable from background conditions and (b) are consistent with timing and location of Rainmaker’s flare releases, called “seeding signatures.”
Detection of a seeding signature establishes clear evidence that flare release directly increased hydrometeor growth and/or precipitation rates. This methodology is inspired by Tessendorf et al., 2019.
Step 2: Quantitative Precipitation Estimation (QPE)
After detection of a seeding signature, radar reflectivity values can be converted to precipitation rates using a power-law relationship called a Z–S relationship: Z=aSb. Here, Z is radar reflectivity; S is the instantaneous snowfall rate (measured as a liquid water equivalent); and the a and b coefficients vary with the type of snow.
Many Z–S relationships are established in scientific literature. Each carries substantial uncertainty; they come from different geographic locations, are derived with different methods, and can change throughout a single storm. Thus, no single Z–S relationship is best suited for Rainmaker’s platform. For this reason, we use an ensemble approach inspired by Friedrich et al. 2020, employing 27 different Z–S relationships to generate a range of possible values.
Each Z–S relationship is applied at each radar pixel, producing 27 instantaneous snowfall rates per signature per scan. These rates are integrated over time and summed over each seeding signature area to produce 27 total volume estimates of water produced. Within this range, Rainmaker reports the mean and the 5th, 25th75th, and 95th percentile estimates.
What Our Study Found
During the 2025–2026 season, Rainmaker's drones released silver iodide flares into winter weather systems. Our team then tracked each seeded area using both operational and research weather radars, using a deliberately conservative approach for seeding signature identification. The results were consistent from operation to operation and found:
- 71 seeding signatures across 15 operational periods, the largest single-season catalog of drone seeding signatures published to date.
- A repeatable timeline. Seeding showed up on radar about 18 minutes after release, peaked around 33 to 36 minutes, and stayed visible for about 51 minutes.
- About 430 acre-feet of precipitation associated with the seeding signatures, or roughly 140 million gallons of radar-estimated liquid water.
Together, these results provide strong evidence that Rainmaker's UAS cloud seeding enhanced precipitation and that the precipitation was quantifiable via radar-based QPE.
The large catalog of seeding signatures also allowed for something new: statistical analysis of seeding signatures as a population. That analysis covered their typical timing, lifetime, size, and motion with the wind, along with a preliminary investigation on the relationship between signature characteristics and atmospheric conditions.
Why It Matters
Rainmaker’s mission is to make Earth more habitable by providing water for the places and people who need it most. In order to accomplish this, we must provide transparent and scientifically rigorous proof that our technology works. Community stakeholders, including water managers, water users, and public agencies, deserve a high level of evidence before they invest in our services.
Rainmaker will continue to push the science of weather modification forward. We look forward to publishing our future research and results.