Radar-Observed Cloud Seeding Signatures from UAS-Based Glaciogenic Seeding: The 2025–2026 Rainmaker Season

Cloud seeding can enhance precipitation, but attributing precipitation to individual seeding events remains difficult in operational programs. We analyze 71 radar-observed seeding signatures from 15 intensive observing periods using a conservative attribution protocol. We ask 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. To our knowledge, this is the largest single-season catalog of UAS seeding signatures and the first large enough to characterize timing, magnitude, geometry, and persistence statistically. Operational UAS seeded three U.S. programs during the 2025–2026 Rainmaker season. Median initial detection occurred 18 min after seeding, followed by peak reflectivity at 33 min, peak precipitation rate at 36 min, and maximum area at 42 min; median radar-detectable lifetime was 51 min. A 27-member reflectivity–snowfall ensemble adapted from SNOWIE estimated 10.42–23.02 acre-feet for PDT-025, while summed ensemble means across 15 IOPs yielded 430.44 acre-feet of signature-associated, radar-estimated liquid-equivalent precipitation. Ensemble spread represents uncertainty among selected reflectivity–snowfall relations, not between the lowest usable radar beam and the surface. The convergence of timing, location, motion, morphology, repetition, and supporting observations provides strong evidence that UAS seeding initiated these enhancements.