Explainer

Who’s doing what — California weather modification

Winter orographic cloud seeding — releasing ice-forming particles into already stormy clouds so more water freezes and falls as snow or rain — has been practiced in California since the early 1950s. It is a reported water-supply tool run by irrigation districts, water agencies, and utilities. Separately, NOAA and EPA records also name a private sulfur-dioxide balloon company that is actively deploying (Make Sunsets), an Israeli–U.S. company building an aircraft SAI system that has not deployed (Stardust Solutions), and a University of Washington sea-salt spray test on the USS Hornet in Alameda. Those are different actors, substances, and means. None of this is secret spraying, and none of it is the white streaks behind jets.

Open the California weather-modification map. Filter by company / operator and by means. Pins are published sites. Shaded boxes are approximate project or reported-region areas. Amounts and methods appear only when a cited report states them.

On this page: Why agencies and PG&E seed · Who pays · Program detail · Dated list · Directory

Three different activities — do not merge them

A reader who heard “Alameda” and “weather modification” together is almost certainly thinking of the Hornet sea-salt test, not Make Sunsets. Primary sources put Make Sunsets’ office at 514 Americas Way #18412, Box Elder, SD 57719 (company contact page and the EPA §114 letter). The two projects share a NOAA reporting statute, not an operator, substance, or launch site.

Commercial SAI / SRM — two companies, different status

Public reporting on for-profit stratospheric aerosol injection is essentially two companies. This site does not invent a third. EPA’s geoengineering FAQ (as of July 2025) said the U.S. government is not doing outdoor solar-geoengineering testing or large-scale deployment, and that EPA was then aware of only one private-sector actor — Make Sunsets — that had actively deployed SAI or MCB in the United States. The same FAQ noted that a few other private actors were developing different solar-geoengineering technologies. Stardust is the other commercial name that later reporting treats as the serious builder (aircraft + proprietary particles), not a balloon deployer.

• Make Sunsets, Inc. — deploying. High-altitude SO₂ balloons; sells cooling credits; NOAA Form 17-4 on file; EPA Clean Air Act §114 demand April 2025. Founder said California and Nevada launches; exact lots often unpublished. Mapped as an approximate South Bay box only.
• Stardust Solutions — R&D, not deploying. Israeli–U.S. for-profit, Delaware-incorporated, headquarters outside Tel Aviv (stardustsrt.com). Developing aircraft systems to disperse proprietary reflective particles — not SO₂ balloons. About $75 million raised ($15 million seed + $60 million in October 2025 led by Lowercarbon Capital: Heatmap, Axios, POLITICO/E&E). Indoor work; October 2025 reporting described “outdoor contained” tests as soon as April 2026 with particles inside a modified plane at about 18 km — not an open free release. The Atlantic (April 2, 2026) wrote that the company said it has no outdoor tests planned until relevant regulations exist. No public California coordinates, so there is no map pin.
• Not SAI companies: California cloud seeding (silver iodide, water agencies) is a separate precipitation tool. The UW Hornet test is marine cloud brightening with sea salt — research, city-blocked restart. Academic proposals such as Harvard’s cancelled SCoPEx balloon experiment are not commercial deployers and are not on this California map.

Dated efforts — newest first

A reference list of reported California weather-modification activity with a published date or season, sorted by that date descending. After- action months (Form 17-4A / agency annual) are not mixed up with Form 17-4 prior notice. If a source only names a season, that is what the date column says. Calendar days appear only when a cited report names them — Mokelumne’s November 2025 17-4A, for example, says one modification day without naming the day of the month.

Full directory of named companies and operators

Every CA-relevant name found in the NOAA filings, DWR / agency reports, EPA pages, and WMA assessments used for this site — not a short sample. Role is listed as operator, sponsor, contractor, site host, funder, host, or government tracker. If someone appears only as a funder, that is said. This roster can still be incomplete: NOAA’s public archive lags, and GAO found underreporting. It does not omit known names to stay short.

41 named entities in this compilation, grouped by role. Click a name to open the matching map filter where a feature exists.

This is not contrails

NOAA’s weather-modification library FAQ answers the question “What if I see streaks in the sky and I think someone is modifying the weather?” directly: those streaks are contrails — condensed combustion products and water vapor from aircraft at high, cold altitudes, observed since the early jet age. NOAA does not regulate airplane exhaust. The EPA sets aircraft emission standards; the FAA administers them. Cloud seeding, by contrast, is a separately reported activity: NOAA must receive Form 17-4 at least 10 days before starting, and operators file Form 17-4A after operations. The map on this site plots those reported programs, not flight tracks.

Source: NOAA Central Library — Weather Modification Project Reports (FAQ: “What if I see streaks in the sky…”).

Most-used substance: silver iodide

California and other western U.S. winter programs almost always use silver iodide (AgI). DWR’s Precipitation Enhancement Resource Management Strategy says projects “generally use silver iodide as the active seeding agent, supplemented by dry ice if aerial seeding is done.” Silver iodide can be released from ground generators or from airplanes. DWR also notes that liquid propane has occasionally been used, and that some recent projects have applied hygroscopic (water- attracting) materials as supplemental agents.

SAWPA’s 2023–24 annual report states that silver iodide was selected “for its environmental safety and superior efficiency in producing ice in clouds,” and that AgI particles have a structural similarity to natural ice. Santa Barbara County’s 2023–24 NAWC report describes high-output silver iodide complex flares at AHOGS sites (about 20 grams of AgI per flare that season). TID’s public program page describes aircraft flares that emit silver-iodide particles.

Dry ice (solid carbon dioxide) and other agents appear in DWR’s general description of California practice. This compilation did not find a California NOAA filing or agency annual report that published a dry-ice tonnage for a recent mapped season, so dry ice is not shown as a separate mapped substance. If a Form 17-4 names another agent, it belongs on the map only after that filing is cited.

Sources: DWR Precipitation Enhancement RMS; SAWPA 2023–24 annual report; Santa Barbara County / NAWC 2023–24 annual report; TID cloud seeding.

Why water agencies and PG&E cloud-seed

Almost every California pin on this map is winter orographic cloud seeding — silver iodide released into storms that are already hitting the mountains. That is a different activity from balloon or aircraft solar radiation modification (Make Sunsets, Stardust R&D). Water agencies and PG&E publish the same purpose in their own reports: grow snowpack or rain so more water later reaches reservoirs, canals, and — for the utility — hydroelectric plants.

Purpose: more runoff, not a statewide weather switch

The DWR Precipitation Enhancement Resource Management Strategy (Water Plan Update 2023, October 2024 imprint) is blunt: “In California, all precipitation enhancement projects are geared toward increasing water supply or hydroelectric power.” DWR describes winter orographic seeding — wind lifting moist air over mountains — as a way to add a modest amount of water to basins that already receive storms. Estimates of extra precipitation or runoff range from about 4% to 15%. DWR also says those percentages are hard to prove in any one year because weather varies so much, and that independent scientific confirmation of contractor claims is still limited.

Operators on this roster name the extra water for:

• Water supply for cities, farms, and groundwater recharge. SAWPA’s Santa Ana program is precipitation enhancement for runoff and snowpack. The Kings River notice targets inflow to Pine Flat Reservoir. Santa Barbara County Water Agency seeds watersheds that feed Twitchell, Cachuma, and Gibraltar so local reservoirs get more runoff.
• Irrigation, environmental flows, and hydropower on the same rivers. Turlock and Modesto Irrigation Districts describe the Tuolumne program as increasing snowpack for those three uses (TID program page).
• Hydroelectric generation in Sierra watersheds PG&E manages or benefits from. PG&E’s Lake Almanor and Mokelumne notices, and the matching NOAA Form 17-4 filings, state the purpose as increasing useful precipitation for hydroelectric / water. DWR notes both programs have run since 1953. That is more water through existing dams and powerhouses when snow melts — not a separate “climate engineering” fleet.

Agencies also argue it is cheaper than imported water when it works. Santa Barbara County hydrologist Matt Scrudato told Noozhawk the county program generated water at an estimated $80 per acre-foot — an agency / press claim, not a DWR audit. DWR’s own statewide cost range is about $20 to $40 per acre-foot of extra water, depending on the watershed and whether seeding is ground or aerial (RMS). Additional water from seeding is treated as natural supply for water-rights purposes, DWR writes.

Why winter storms in the mountains

California’s large programs are timed to winter orographic storms — moist air already being lifted over the Sierra Nevada, Transverse Ranges, or Peninsular Ranges. DWR: this has been practiced in California since the early 1950s. Ground generators (CNG or AHOGS) and, on some projects, aircraft release silver iodide into that existing cloud. The intended result is more snow in the high country that melts into streams in spring, or more rain in a coastal watershed that runs into a reservoir. PG&E’s current notices cover roughly November through May. That is drought-resilience and local supply augmentation in named basins — not an attempt to steer weather across the state. DWR notes that agencies often suspend seeding in wet years once enough snow has piled up.

What they are not doing

• Not SO₂ balloon SAI. Make Sunsets is a separate company selling cooling credits and filing under NOAA as solar-radiation modification. Water agencies and PG&E are not that program.
• Not secret spraying. Operators file NOAA Form 17-4 (prior notice) and 17-4A (after-action). DWR’s RMS adds California rules: an initial notice of intent, then every five years for continuing projects; some record-keeping; annual or biennial reports to DWR; CEQA review; and annual letter notices to affected county boards of supervisors. The Kings 2023–24 packet is one public example, and it lists PG&E as a collaborator on that river, not a covert sponsor.
• Not “controlling California’s weather.” The published purpose is incremental snow or rain in a named watershed so more of an existing storm becomes runoff later. DWR treats that as one small tool next to storage, conservation, and groundwater — not a statewide thermostat.

Who pays — and how much is public money

Dollar figures below appear only when a cited report or contemporaneous news story states them. They are not added up into a statewide total here. DWR’s own range is the only statewide number. Labels:

• State grant (taxpayer) — California DWR money. DWR’s RMS says it does not directly fund day-to-day operations; it tracks programs and recommends State support. The SAWPA pilot is the named recent grant.
• Local public agency / water district (ratepayer or local tax) — irrigation districts, county water agencies, joint-powers authorities, and their member purveyors. Paid from agency budgets that come from water rates, assessments, or local taxes.
• Investor-owned utility (ratepayer-regulated) — PG&E. This is not a state or federal spray budget. Costs sit in the utility’s hydro / water operations. That is not the same as a taxpayer line item, even though residential customers ultimately fund the utility.
• Private — Make Sunsets cooling-credit sales and venture money. Not public cloud-seeding funds.

Statewide (DWR)

DWR estimates roughly $5 million to $7 million a year on California cloud-seeding operations (RMS cost section). That is DWR’s statewide range, not a sum of the programs on this map. Federal money “has been scarce for the last 25 years,” DWR writes. Local agencies typically bundle costs or look to local bonds and water pricing. A hypothetical expansion that could add 500,000 to 700,000 acre-feet would take about $18 million up front plus about $8 million a year — DWR’s planning figure for more programs, not current yield.

Named program budgets

• SAWPA Santa Ana pilot — ~$1.2 million planned four-year cost. About half from a California DWR grant (state taxpayer / public funds). The remainder was split evenly among SAWPA’s five member public water agencies (local ratepayer / agency budgets). LA Times Daily Pilot, Jan. 13, 2024 (quoting SAWPA’s Jeff Mosher). SAWPA’s own FAQ also said the DWR grant covered half. The pilot concluded July 10, 2025 after year-1 validation found insufficient evidence of a significant precipitation increase, plus burn-scar debris-flow risk. Host sites in SAWPA Table 2-2 include Chino Basin Water Conservation District / WCD, San Antonio Water Company, San Bernardino Valley Municipal Water District, San Bernardino Valley Water Conservation District, San Gorgonio Pass Water Agency, Eastern Municipal Water District, El Toro Water District, East Orange County Water District, and others.
• Santa Barbara County / Twitchell — about $370,000 a year in late-2022 coverage (Noozhawk; San Luis Obispo Tribune; Santa Barbara Independent, Dec. 29, 2022). County Water Agency about 50%; the rest split among about nine local water purveyors (Carpinteria, Montecito, Santa Barbara, Goleta, Santa Ynez Valley, Santa Maria, and others named in that coverage). Local public agency / ratepayer money. Contractor: NAWC, since 1981. Older board contract: 2018–19 NAWC agreement not to exceed $146,500 (County of Santa Barbara File 18-00807). The $80/acre-foot figure above is the county hydrologist’s cost-effectiveness claim in that same press, not a published audited yield.
• Kings River — $475,597 board-approved budget for the 2023–24 season starting Dec. 1, 2023, “in collaboration with Kings River Water Association and Pacific Gas and Electric” (ground generators plus up to 30 hours of aircraft). KRCD Weather Modification Program notice. Local public-agency money (KRCD / KRWA); PG&E is a collaborator, not the sole funder. A WMA economic paper also lists KRWA, PG&E, and DWR among historic supporters. That $475,597 is the approved project budget on that notice — not a claim that every dollar was spent.
• Tuolumne (TID / MID) — published as a maximum $475,000 in CNBC, Dec. 17, 2022, for Turlock’s program (3–5% runoff increase claimed in that story). Older local coverage put the shared TID + MID cost at about $165,000–$170,000 a year (San Francisco Chronicle; Turlock Journal— the Journal piece is from the program’s “22nd year,” so about 2012 if the start year is 1990). Local irrigation-district (ratepayer) money. Contractor: Weather Modification International. Current-season actual spend is not on the TID page used here.
• PG&E Lake Almanor and Mokelumne — budget not published in the DWR RMS, NOAA 17-4 / 17-4A PDFs, or CPUC filings used for this site. The San Francisco Chronicle (2015 drought coverage) wrote that PG&E’s program “costs a couple of hundred thousand dollars annually” and that the company declined to provide a specific amount. Treat that as a press paraphrase, not a published line item. Funder: investor-owned utility. A WMA paper lists East Bay Municipal Utility District among historic Mokelumne supporters.
• SMUD Upper American — current-season budget not published in the sources used here. DWR cites a Water Year 2020 SMUD / RHS Consulting winter report (streamflow-increase estimates only).
• Make Sunsets — private, not public cloud-seeding money. NPR (April 2024) reported more than $1.2 million from Boost VC, Pioneer Fund, and Draper Associates, plus cooling-credit sales. That does not fund PG&E or water-agency generators.

Major California programs

Status, means, and amounts only where a cited filing or agency report states them. “Listed” means a WMA or DWR mention without a current after-action report in this compilation.

Santa Ana River Watershed (SAWPA) — ended

Years: four-year pilot planned Nov. 15, 2023–Apr. 15, 2027; operated winter 2023–24; concluded July 10, 2025. Target: Santa Ana River Watershed (San Gabriel, San Bernardino, San Jacinto, and Santa Ana mountains). Means: ground CNG and AHOGS; no aircraft in 2023–24. Substance: silver iodide — 17,082 g from CNG hours and 640 g from 32 AHOGS flares; 13 seeded storms over 22 days (SAWPA 2023–24 annual). Operator: NAWC. Sponsors: SAWPA and member / host agencies. Money: ~$1.2 million planned; ~half DWR grant, rest five member agencies. Outcome: SAWPA said year-1 validation did not show a strong enough precipitation increase; 2024 burn scars would have forced another suspension.

Santa Barbara County / Twitchell — operating

Years: county Water Agency program since 1981 (research in the area dates earlier). Last confirmed seeded days: early April 2024 (2023–24 NAWC annual). Target: Twitchell Reservoir and, when active, Lake Cachuma / Santa Ynez / Gibraltar. Means: AHOGS (three active in 2023–24: Mt. Lospe, Harris Grade, Berros Peak) plus aircraft in some years; 2023–24 was ground-only. Substance: silver iodide — about 3,180 g from 159 flares; 14 storm events on 19 calendar days (2023–24 annual). Operator: NAWC. Sponsors: SBCWA plus local purveyors. Money: ~$370k/year in 2022 coverage; 2018–19 NTE $146,500. 2025CASB-1 noticed 2024–25; the only posted 17-4A (December 2024) is zero days.

Kings River (KRCD / KRWA) — operating

Years: 1954–55–present (KRCD / JWM histories); WY2025 operations ended Apr. 15, 2025 per KRCD. Target: Kings River inflow to Pine Flat Reservoir (2,225 sq mi on Form 17-4 2024WYKI-1). Means: aircraft plus ground silver-iodide generators (2023–24 notice: ground + up to 30 hours aircraft). Operator: RHS Consulting on the 2024 17-4. Sponsors: KRCD and KRWA; PG&E collaborator on the 2023–24 notice. Money: $475,597 board-approved 2023–24 budget. Season grams for WY2025 were not posted; KRCD said it was waiting on the final report.

Tuolumne River (TID / MID) — operating (noticed)

Years: TID since 1990; Form 17-4 2026WYUT-1 notices Nov. 1, 2025–Apr. 30, 2026. Target: Tuolumne River Watershed (675 sq mi on 2025WYUT-1). Means: aircraft AgI flares (WMI). Sponsors: Turlock and Modesto Irrigation Districts. Money: CNBC 2022 max $475,000; older press ~$165–170k/year. No posted 17-4A of actual 2025–26 days or grams. TID’s page claims a potential 5–15% precipitation increase and names irrigation, environmental flows, and hydropower as the uses.

PG&E Mokelumne — operating; newest posted seeding

Years: since 1953 (DWR / PG&E). Newest after-action: November 2025. Target: Mokelumne watershed, about 170 sq mi (Calaveras, Amador, Alpine). Means: seven ground-based, radio-controlled propane-acetone AgI generators at 21.5 g/hour (Form 17-4; site coordinates not published). Substance: November 2025 — 1 modification day, 83 ground hours, 1,760 g AgI (Form 17-4A 2026CAMOKE-2). December 2025: 0 days. Operator / sponsor: PG&E. Money: budget not published in sources used; Chronicle paraphrase “a couple of hundred thousand” / declined a specific figure. Purpose: hydroelectric / water.

PG&E Lake Almanor — operating (no recent NOAA PDF found)

Years: since 1953. Target: Lake Almanor, Butt Valley, and Mountain Meadows watersheds (Plumas, Lassen, Tehama). Means: ground-based AgI generators (2011 NOI: November–May). Money / grams: not published in the DWR RMS or the NOI text used here. No 2024–2026 Almanor Form 17-4 / 17-4A under the posted California filenames. DWR notes silver sampling in water, sediment, and fish at Lake Almanor (2000–2003) was far below toxic levels.

SMUD Upper American — listed (2020 report only)

DWR cites a Water Year 2020 SMUD / RHS Consulting winter report: streamflow up 13% over the basin and 20% in the primary target — the cited study’s estimates, not a current-season after-action. Current operator, means, grams, and budget are not confirmed in that paragraph.

San Joaquin and Carson / Walker — listed only

WMA economic assessments list a San Joaquin winter program (historic SCE among sponsors) and Carson/Walker snowpack work. Current-season operator, hours, grams, and budgets were not in the sources compiled for this map.

How ground generators work

California ground programs use two machines that do the same job in different ways: put microscopic AgI particles where wind will carry them into supercooled cloud.

Cloud Nuclei Generators (CNG)

SAWPA / NAWC describe a CNG as a propane-fueled unit that holds a silver iodide solution. When the unit is lit, the solution burns and the plume carries AgI particles into the air. SAWPA’s 2023–24 report says the solution is designed as a fast-acting nucleation agent (condensation-freezing) rather than slower contact nucleation — useful where mountain barriers are relatively narrow. Most SAWPA CNGs were operated by people at the host site (water-agency staff or landowners) after a meteorologist called for operations. One unit was run remotely. NAWC’s 2021 feasibility report recommended on the order of 20–25 grams of silver iodide per hour of CNG operation as a design rate — a recommendation, not a measured 2023–24 total.

AHOGS (Automated High Output Ground Seeding)

AHOGS units are remote flare trees. SAWPA and Santa Barbara reports describe a camera, battery, and cellular / modem control so a project meteorologist can ignite high-output AgI pyrotechnic flares from an operations center. Flares burn in place for a few minutes and release a dense burst of particles — intended for convective rain bands, where a continuous CNG plume may be too slow. Santa Barbara’s 2023–24 report says each AHOGS holds two masts and a total of 32 fast-acting flares, with spark arrestors over the flares. SAWPA used three AHOGS in 2023–24 (El Toro WD reservoir, East Orange County WD, and an EMWD booster); Santa Barbara used three active AHOGS for Twitchell (Mt. Lospe, Harris Grade, Berros Peak).

Aircraft seeding, when used, releases AgI from wing-tip solution generators or burn-in-place flares upwind of the target so crystals can grow and fall inside the watershed. TID’s page describes flying into the storm to test conditions, then igniting flares if the storm qualifies. SAWPA’s 2023–24 season was ground-only. Santa Barbara’s 2023–24 season was also ground-only; the county program design still includes aircraft in some years.

NOAA reports. It does not regulate.

The Weather Modification Reporting Act of 1972 (15 U.S.C. § 330 et seq.) and 15 CFR Part 908 require anyone conducting weather modification in the United States to file an initial report (Form 17-4) that NOAA must receive at least 10 days before activities start (15 CFR § 908.4), then file interim and final reports (Form 17-4A) afterward. That is prior notice, not a filing due within 10 days of any spraying. That reporting net is wider than winter cloud seeding. 15 CFR § 908.3(a)(3) expressly covers “modifying the solar radiation exchange of the earth or clouds, through the release of gases, dusts, liquids, or aerosols into the atmosphere.” EPA’s geoengineering pages point to the same rule. Make Sunsets’ 2023 Form 17-4 and the UW Hornet 2024CACARE-1 filing sit under that statute alongside AgI cloud-seeding 17-4s. GAO-26-108013 notes that finals are due no more than 45 days after activity ends, matching 15 CFR § 908.6. File both forms by email to weather.modification@noaa.gov. NOAA posts those filings on the Weather Modification Project Reports library page, usually within about two months after the end of the fiscal quarter. NOAA’s own FAQ says it does not research or conduct weather-modification experiments, and that it collects information but does not regulate cloud seeding.

GAO-26-108013 (February 2026) found that NOAA is not fully meeting its duty to maintain and share those reports. GAO reviewed a sample of the public archive and described it as incomplete, inconsistent, and unreliable: some submitted reports never appeared; the earliest record in the online database as of late 2025 was from 1999 even though the Act dates to the early 1970s; and four of ten states with publicly described 2021–2025 activities had some of those activities missing from NOAA’s database. GAO also estimated that more than half of filed reports likely have errors, including missing required information such as maps. NOAA agreed with GAO’s recommendations.

This map is therefore a compilation of reported activities from agency reports, DWR, and the NOAA reporting program. It may be incomplete. A structured 2000–2025 extract of NOAA PDFs is published on Zenodo (DOI 10.5281/zenodo.14925812) and described in Donohue & Lamb, arXiv:2505.01555. This compilation used that CSV (223 California rows; record updated 2025-07-10) to find NOAA filenames, then pulled newer 2026 PDFs from the NOAA library that post after the extract.

On the map, red is reserved for the newest posted after-action seeding — the latest month on a Form 17-4A or agency annual with modification days greater than zero. As of this compilation that is PG&E Mokelumne in November 2025 (Form 17-4A 2026CAMOKE-2: 1 day, 83 ground hours, 1,760 g silver iodide). A 2026 Form 17-4 initial (for example Tuolumne 2026WYUT-1) is prior notice only and stays the older color until an after-action report lists actual days.

What this map includes — and what it cannot

• santa-ana — 2023–24 operations; program ended July 10, 2025. 15 published generator sites + approximate watershed. No 2025–26 season.
• santa-barbara — 1981–present (NAWC/SBCWA); last confirmed seeded days early April 2024. 6 published AHOGS sites (3 active 2023–24). 2025CASB-1 noticed 2024–25; Dec 2024 17-4A reported 0 days. No 2026CASB found.
• kings — 1954–55–present; KRCD WY2025 operations ended Apr. 15, 2025. Approximate Pine Flat watershed. 2024WYKI-1 Form 17-4 on file; no 2025/2026 NOAA PDF found; WY2025 final not posted.
• tuolumne — TID since 1990; 2026WYUT-1 notices Nov. 1, 2025–Apr. 30, 2026. Aircraft AgI flares (WMI). 2026 initial is prior notice; no 17-4A of actual 2025–26 days posted.
• almanor — PG&E since 1953. Approximate target; no 2024–2026 Almanor NOAA PDF found under posted CA filenames.
• mokelumne — PG&E since 1953; red = most recent posted seeding (Nov. 2025). Approximate 170 sq mi target. 2026CAMOKE-1 (17-4) and 2026CAMOKE-2 (17-4A interim). No published generator coordinates.
• san-joaquin — Listed in WMA assessments; current season not confirmed here. Approximate area only
• american — DWR cites SMUD / RHS Water Year 2020 report. Approximate area only
• walker — Listed in WMA assessments; current season not confirmed here. Approximate CA-side box only
• make-sunsets — 2022–present (company); 2023 NOAA 17-4 on file; EPA §114 Apr. 2025. SO₂ balloons / cooling credits. HQ Box Elder, SD — not Alameda. Approximate Silicon Valley box only; exact lots unpublished. Separate from the UW Hornet sea-salt test.
• uw-hornet-mcb — March–April 2024 sprays; city rejected restart June 4, 2024. Sea-salt MCB spray on the USS Hornet, Alameda. NOAA 2024CACARE-1. Different actor, substance, and means from Make Sunsets.

• No California Form 17-4A with seeded days after November 2025 was posted. Mokelumne’s season is noticed through May 31, 2026; Tuolumne through Apr. 30, 2026. Those later months may still be in NOAA’s ~2-month-after-fiscal-quarter posting lag.
• No 2026CASB, 2026WYKI, or 2026 Almanor PDF was found on the NOAA oarcloud paths that hold the Mokelumne and Tuolumne 2026 files.
• Santa Barbara 2024–25: Form 17-4 exists; the only posted 17-4A (December 2024) is zero days. A full-season 17-4A / 2024–25 annual was not found.
• Kings WY2025 ended Apr. 15, 2025 per KRCD; the final report KRCD said it was waiting for is not in the NOAA filenames checked.
• NOAA Form 17-4 / 17-4A PDFs are the federal filings, but the public library table is incomplete (GAO-26-108013). This map is not a complete extract of every California 17-4 on file.
• Zenodo DOI 10.5281/zenodo.14925812 (updated 2025-07-10) has 223 California rows in cloud_seeding_us_2000_2025.csv. It includes 2025CASB-1, 2025WYUT-1, and 2025CAMOKE-1. 2026CAMOKE and 2026WYUT PDFs were posted after that extract and are cited from the NOAA library directly.
• Ground-generator coordinates are published for SAWPA 2023–24 (Table 2-2) and Santa Barbara AHOGS (Table 4-1) only. Mokelumne’s seven named 2024–25 burners have no published coordinates and are not plotted as pins.
• Amounts of AgI are included only where a Form 17-4A or agency annual published them (Mokelumne 17-4As; SAWPA 2023–24; Santa Barbara 2023–24).
• Rockets were not found in the California NOAA filings or agency reports used for this map; they are listed as a means filter with no features.
• Make Sunsets exact launch coordinates are not on the 2023 Form 17-4 or the EPA §114 letter. The South Bay box is an NPR-described region only. HQ is Box Elder, SD, not Alameda. Nevada launches named by the founder are off this California map.
• Stardust Solutions has no published California launch or test coordinates and is not plotted. EPA FAQ (July 2025): only Make Sunsets was then known as an active US SAI/MCB deployer; Stardust is R&D / test-prep. Do not invent a CA pin.
• This compilation does not invent other SAI companies. Public reporting on the commercial SAI field is essentially Make Sunsets (deploying SO₂ balloons) and Stardust (building an aircraft / particle system). Harvard SCoPEx and similar academic proposals are not commercial deployers and have no CA pin here.
• The UW Hornet pin uses published National Register coordinates for the museum ship, not a surveyed spray-nozzle location. Do not merge that pin with Make Sunsets.
• Dry ice and hygroscopic agents are mentioned generally by DWR for some aerial / supplemental work; no recent CA 17-4A compiled here named a dry-ice total, so they are not mapped as separate substances.
• The 2025 DWR RMS URL hosts the Water Plan Update 2023 Precipitation Enhancement strategy (October 2024 imprint). It does not include a machine-readable table of every current project.

Sources

• NOAA Weather Modification Project Reports (Forms 17-4 / 17-4A) — Federal reporting archive. File Form 17-4 at least 10 days before activity; file 17-4A afterward at weather.modification@noaa.gov. NOAA collects reports; it does not regulate or permit cloud seeding. Posts usually within ~2 months after the fiscal quarter.
• NOAA Form 17-4A 2026CAMOKE-2 (Mokelumne Nov–Dec 2025) — Newest posted CA after-action report with actual seeding: Nov 2025, 1 day, 83 ground hours, 1,760 g AgI.
• NOAA Form 17-4 2026CAMOKE-1 (Mokelumne 2025–26 initial) — Prior notice: Nov. 1, 2025–May 31, 2026. Seven ground generators at 21.5 g AgI/hour.
• NOAA Form 17-4 2026WYUT-1 (Upper Tuolumne 2025–26 initial) — Prior notice: Nov. 1, 2025–Apr. 30, 2026. Aircraft AgI flares (WMI). No 17-4A posted yet.
• NOAA 2025CASB-1 / FY25 Q2 17-4A (Santa Barbara Twitchell) — 2024–25 initial Dec. 1, 2024–Mar. 31, 2025; Dec 2024 interim reported 0 seeded days.
• 15 U.S.C. § 330 et seq. (Weather Modification Reporting Act of 1972) — Federal reporting statute. Implementing rules: 15 CFR Part 908.
• Structured US cloud seeding dataset 2000–2025 (Zenodo) — LLM extract of NOAA PDFs (record updated 2025-07-10); 223 California rows. Scientific Data / arXiv 2505.01555. 2026 NOAA PDFs are newer than this extract.
• Donohue & Lamb, arXiv:2505.01555 — Methods paper for the Zenodo dataset.
• CA DWR Precipitation Enhancement RMS (2025 URL / Water Plan Update 2023) — All CA projects geared to water supply or hydro. Statewide ~$5–7M/year; ~$20–40/AF. Winter orographic since early 1950s. NOI every five years.
• LA Times Daily Pilot — SAWPA $1.2M / DWR grant (Jan. 13, 2024) — Four-year Santa Ana pilot ~$1.2M; about half DWR grant; remainder split among five member agencies (Mosher).
• Noozhawk — Santa Barbara cloud seeding — ~$370k/year; Water Agency ~50%; ~nine purveyors; $80/AF agency/press claim.
• San Luis Obispo Tribune — Santa Barbara program — Same $370k / 50% county split as Noozhawk.
• Santa Barbara Independent — $370k (Dec. 29, 2022) — Board voted $370,000 for the season; NAWC contractor.
• Santa Barbara County File 18-00807 — 2018–19 NAWC agreement not to exceed $146,500.
• KRCD Weather Modification Program notice (2023–24) — Board-approved budget $475,597; KRWA and PG&E collaborators; ground + up to 30 hrs aircraft.
• CNBC — Western cloud seeding (Dec. 17, 2022) — TID program maximum budget $475,000; 3–5% runoff claim in that story.
• SF Chronicle — drought-era seeding costs — TID/MID about $165,000; PG&E 'couple of hundred thousand' and declined a specific amount.
• Turlock Journal — TID/MID ~$170k/year — Shared TID+MID cost about $170,000/year; WMI contractor. Program's 22nd year (~2012).
• SAWPA Annual Cloud Seeding Report 2023–24 — 15 sites, CNG/AHOGS description, 17,082 g + 640 g AgI.
• SAWPA program concludes (July 10, 2025) — Pilot ended after validation report; burn-scar suspension risk.
• Turlock Irrigation District cloud seeding — Aircraft AgI flares, Tuolumne watershed, since 1990, with MID.
• GAO-26-108013 — NOAA public database incomplete vs some state filings; NOAA does not regulate.
• GAO-26-108013 PDF — Four of ten states with 2021–2025 public activities had some activities missing from NOAA’s database.
• 15 CFR Part 908 — Weather Modification Reporting Act implementing rules.
• Santa Barbara / Twitchell CEQA MND (WMA) — County program since 1981; ground and aircraft AgI.
• Kings River JWM evaluations — Long-running KRCD program; NAWC since 2008.
• WMA economic assessment of western programs — Lists Almanor, Mokelumne, Tuolumne, San Joaquin, Kings, Carson/Walker, Santa Barbara, and others.
• 15 CFR § 908.3 — activities subject to reporting — Includes modifying solar radiation exchange through release of gases, dusts, liquids, or aerosols — not only cloud seeding.
• EPA news release — CAA §114 demand to Make Sunsets (Apr. 15, 2025) — Office of Air and Radiation information demand; SO₂ balloons and cooling credits.
• EPA Government Action (geoengineering) — Make Sunsets ~0.1 tons SO₂ as of May 2025; WMRA / 15 CFR 908.3 SRM reporting.
• EPA Frequent Questions (geoengineering) — As of July 2025, EPA was aware of only one private actor (Make Sunsets) that had actively deployed SAI or MCB in the United States; other private actors were developing technologies. US government not deploying SRM.
• Stardust Solutions — Company site; May 2026 papers on amorphous silica and particle dispersal. No CA launch map.
• Heatmap — Stardust $60M (Oct. 24, 2025) — Lowercarbon-led round; prior $15M seed; will not deploy until governments authorize (CEO).
• MIT Technology Review — Stardust (Dec. 10, 2025) — Ness Ziona HQ; aircraft + proprietary particles; contrasts with Make Sunsets balloons.
• POLITICO / E&E — Stardust $60M and contained aircraft tests — Delaware-incorporated; HQ outside Tel Aviv; ~$75M total; April 2026 in-plane tests at ~18 km described as contained, not free release.
• The Atlantic (Apr. 2, 2026) — Company: R&D not deployment; no outdoor tests planned until regulations.
• Wikipedia — Stardust Solutions — Secondary summary of incorporation, funding, and 2026 papers.
• Harvard / Keutsch Group — SCoPEx — Academic SRM experiment; not a commercial deployer; not on the CA map.
• EPA CAA §114 letter to Luke Iseman and Andrew Song — Addressed to 514 Americas Way #18412, Box Elder, SD 57719.
• NOAA Form 17-4 2023wmainitial (Make Sunsets / Cooling Earth) — Handwritten initial; balloon SAI; HQ Box Elder on the form.
• NOAA Form 17-4 2024CACARE-1 (UW / Hornet sea-salt study) — Field study of controlled-release sea salt aerosol plume; UW and SRI; Hornet host letter.
• Make Sunsets contact information — Published HQ: Box Elder, South Dakota — not Alameda.
• Make Sunsets FAQ — Company claims U.S. activity falls under the Weather Modification Act and yearly NOAA reporting.
• NPR — solar geoengineering, Make Sunsets and Hornet (Apr. 21, 2024) — Witnessed Silicon Valley-outskirts balloon launch and, separately, Hornet sea-salt spray.
• Inside Climate News — EPA targets Make Sunsets (Apr. 18, 2025) — Founder said balloons are released in California and Nevada; 2024 NOAA report not yet posted.
• City of Alameda statement (June 5, 2024) — Council unanimously rejected UW sea-salt studies on the USS Hornet.
• City of Alameda File 2024-4063 — Landlord consent item; 707 West Hornet Avenue; salt-water spray.
• USS Hornet Museum directions — 707 W Hornet Ave, Pier 3, Alameda.

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