CWOP and APRS: Share Your Weather Station With NOAA
A weather station on the roof is one of the oldest ways for amateurs to combine radio, electronics and a useful public service. A CWOP APRS weather station goes a step further: it reports its measurements automatically, and the data may end up in the same systems that feed weather forecasts. CWOP, the Citizen Weather Observer Program, began with amateur radio operators experimenting with packet radio, and it still has strong ties to APRS. This guide explains what CWOP is, how the data travel from a backyard sensor to the National Weather Service, what role APRS and the internet play, how to place the sensors so that the readings are worth sharing, how quality control works and how to join. The facts come from the reference article on the Citizen Weather Observer Program and from the program’s own site.
What CWOP Is
According to the reference, CWOP is a network of privately owned electronic weather stations, concentrated in the United States but also located in more than 150 countries. Volunteers with computerized weather stations send automated surface weather observations to the National Weather Service through the Meteorological Assimilation Data Ingest System, known as MADIS. The data are then used by forecast models, and the observations are also redistributed to the public. The article reports that as of September 2026 more than 13,000 stations worldwide report regularly to the network.
The program’s own website, wxqa.com, describes CWOP as a public-private partnership with three goals: to collect weather data contributed by citizens, to make those data available for weather services and homeland security, and to give the contributors feedback so that they have the tools to check and improve their data quality. The address stands for weather quality assurance, which tells you something about the priority. The site says that the number of North American stations sending data over a few days is normally more than 7,000, sending 50,000 to 75,000 observations every hour, and that over 800 different organizations use the CWOP data.
How the Data Travel
The data path is easy to follow once you separate the radio part from the internet part.
- The station measures. Sensors for temperature, humidity, pressure, wind and rain feed a data logger or a small computer.
- The station reports. The report is formatted as an APRS weather packet. It is either transmitted by radio through an APRS modem or sent directly over the internet.
- An IGate or direct internet connection passes it on. The reference explains that numerous IGates, meaning internet gateways, receive broadcast APRS packets from the radio network and forward them via APRS-IS to the FindU servers. Packets can also originate directly from computers on the internet without being broadcast on the radio waves.
- FindU forwards to MADIS. The wxqa.com site says that every five minutes, the data are sent from the findU server to the NOAA MADIS server.
- Quality checks and distribution. The MADIS system integrates weather observations from many sources and applies temporal and spatial consistency checks. Quality flags are stored with the data so that users can obtain the most trustworthy data possible. From MADIS, the CWOP data are redistributed to other users.
The amateur radio connection, as the reference notes, makes it inexpensive and simple for an individual to install consumer-level weather sensors at a point of interest, connect them to a radio transmitter through a simple APRS modem and start sharing weather reports. Solar power and radio transmission make it possible to place self-contained weather stations at unattended and wireless sites, which allows a dense set of measurements. If you are new to the packet system itself, read our article explaining APRS, IGates and digipeaters first.
Radio or Internet?
CWOP began as an amateur radio experiment, but it now includes both amateur radio APRS stations and internet-only stations. The two options suit different people, and the table compares them.
| Path | What you need | Strengths | Limits |
|---|---|---|---|
| APRS by radio | Amateur radio license, a radio, a TNC or APRS modem, and an IGate within range | Works at sites without internet; fits solar-powered remote stations | Needs a license and an IGate in range; airtime is shared with other APRS users |
| Internet only | A weather station or computer with internet access and software that sends the report | No radio equipment and no license; simple at home | Depends on the connection; does not serve remote sites |
| Radio plus internet | Both of the above, with software that uses each as a backup | Redundant reporting | More setup effort |
The program’s member lists show that the identifiers differ by type. The site allows searches of the member list by ham, CW or DW call sign, which reflects that licensed amateurs report under their call signs and others use a program-assigned identifier. If you are a ham, your call sign with a suffix forms the station identity; otherwise you apply for the assigned identifier when you sign up.
The Radio Side: Packets on VHF
If you choose the radio path, the report goes out on the standard APRS frequency in your region, through a TNC or a sound card modem, and is picked up by IGates and digipeaters. A software modem running on a small computer is enough for many stations. Our article on Direwolf, a soundcard packet TNC explains how to build one with a sound interface, and the guide to Raspberry Pi ham radio projects shows how a single-board computer can run it all day. The APRS reference article lists weather reports as one of the standard packet types, alongside positions, messages and telemetry.
Keep the transmissions modest. Weather reports are short, and a station only needs to send them every few minutes. A weather station that sends a packet every few seconds would waste airtime and annoy other users of the channel. Follow the reporting interval recommended by the program, and use the lowest power that reaches your IGate. A fixed station on a good antenna rarely needs more than a few watts.
Siting the Sensors
A weather station is only as good as its location. The CWOP goal of giving contributors the tools to improve their data would be pointless if the sensors were placed carelessly. The following points reflect standard meteorological practice, and the program’s own resources give more detail on station setup.
Temperature and Humidity
Mount the sensor in a ventilated radiation shield, in the shade, away from walls, roofs, chimneys and air-conditioner exhausts. A sensor in direct sun or next to a hot wall reads too high, and a sensor on a roof reads differently from one over grass. A height of a couple of meters above the ground, over natural ground cover, is the usual target.
Wind
The anemometer and vane need open exposure, high enough to clear obstacles. Trees and buildings disturb the flow, so readings from a sensor next to the house are biased. The reference photograph shows a typical station with a mast supporting the wind vane and anemometer while the rain gauge and other sensors are close to the ground, which reflects the usual compromise.
Rain and Pressure
The rain gauge should be level, in an open area away from overhanging trees and the roof edge, so that it catches rain the way the ground does. Pressure sensors can sit indoors, but the reading must be configured correctly for the station’s elevation, because forecast systems compare station pressure with models. Confirm the setting against a nearby official observation.
Lightning and Grounding
A mast carrying sensors and an antenna is a lightning target. Protect the station with proper grounding and surge protection on the cables, as described in our guide to station grounding and lightning protection. Use waterproof connectors on every outdoor joint.
Data Quality and Feedback
One reason CWOP is respected is its attention to data quality. The reference says that MADIS applies temporal and spatial consistency checks and stores quality flags with the data. The wxqa.com site offers pages for data quality and for checking the packets that stations send, which allows contributors to find problems such as a stuck sensor, a bad pressure setting or a time error. A good habit is to compare your readings with those of nearby stations, particularly when a front passes or after a rain, and to fix any consistent offset at its source rather than adjusting the numbers.
Time is another common problem. Weather observations are valuable because they are timely, so the clock on your logger or computer should be correct and the reports should use the right time reference. Our article on UTC time in ham radio explains the standard time that weather and radio services use.
Typical Equipment
Most CWOP stations are built around a consumer weather station sold for home use, with an outdoor sensor array, an indoor console and a way to read the data into a computer. The outdoor array normally combines temperature and humidity, wind speed and direction, and a rain gauge, and a separate barometer is built into the console or the logger. A small always-on computer, such as a single-board computer, reads the data and runs the software that formats and sends the reports. For a radio station, add a VHF transceiver, an antenna with a clear path to the nearest IGate or digipeater, and a modem, either a hardware TNC or a sound card with software. For an internet-only station, the same computer sends the reports directly. Whichever route you choose, keep the cable runs short, use shielded cable for the sensors where the manufacturer recommends it, and label every connector so that you can service the station without guessing.
Plan for maintenance as well. Rain gauges clog with leaves and insects, radiation shields collect dust and spider webs, and anemometer bearings wear out. A visit every few months to clean and inspect the sensors keeps the readings honest, and a station that suddenly changes behaviour after a storm is a good reason to climb the mast and look.
Joining the Program
The wxqa.com site provides sign-up pages for CWOP and for a snow-observation variant. The general steps are as follows, though you should follow the instructions on the program’s current pages because they are updated from time to time.
- Install and test the station until the readings are stable and sensible, and place the sensors correctly.
- Choose your reporting path: APRS by radio with a licensed call sign, or internet only.
- Read the program’s information pages and the recommended reporting interval.
- Complete the sign-up form with your location, the station type and your contact details, and wait for your identifier.
- Configure the software to send reports to the servers listed on the program’s pages, using the identifier you were given.
- Watch the quality pages for a few days and fix any problems that they show.
Why Hams Take Part
For radio amateurs, the appeal is practical. A weather station gives your APRS setup a purpose beyond a symbol on a map, and the data have a real use: the reference notes that CWOP observations feed forecast models. For emergency-minded hams, local weather data complements storm spotting. Our guide to the high altitude balloon and APRS tracking shows another way that APRS reports atmospheric data, this time from a platform that rises through the sky. Both projects teach the same skills: sensors, packets, gateways and checking your data against the real world.
The Bottom Line
CWOP lets a backyard weather station contribute to the same data stream that supports forecasts. Hams can report with APRS through IGates and the internet servers, and others can report over the internet alone, and the data go from FindU to NOAA’s MADIS every five minutes for quality checking and distribution. Good sensor siting, a correct clock and attention to quality feedback matter more than expensive equipment. Choose your path, place the sensors carefully, sign up on the program’s pages, and keep an eye on the quality reports.
Frequently Asked Questions
What is CWOP?
The Citizen Weather Observer Program is a network of privately owned weather stations that send automated observations to the National Weather Service through MADIS, where they feed forecast models and are redistributed to the public.
Do I need a ham license?
Not for internet-only reporting. A license is needed to send APRS packets by radio, which is how the program began.
How often is the data forwarded?
The program’s site says the data are sent from the findU server to the NOAA MADIS server every five minutes.
What is MADIS?
It is the Meteorological Assimilation Data Ingest System, which integrates weather observations from many sources and applies consistency checks, storing quality flags with the data.
How many stations take part?
The reference article reports more than 13,000 stations worldwide as of September 2026, in over 150 countries, with the site reporting normally more than 7,000 in North America.
Where should I put the sensors?
Use a shaded, ventilated shield for temperature, an open mast for wind, a level open spot for the rain gauge and the correct elevation setting for pressure.