Inside the Lifesaving Power of Doppler Weather Radar

Scientific American

30-05-2025

Outside every National Weather Service (NWS) office around the U.S. stands what looks like an enormous white soccer ball, perched atop metal scaffolding several stories high. These somewhat plain spheres look as ho-hum as a town water tower, but tucked inside each is one of modern meteorology's most revolutionary and lifesaving tools: Doppler radar.
The national network of 160 high-resolution radars, installed in 1988 and updated in 2012, sends out microwave pulses that bounce off raindrops or other precipitation to help forecasters see what is falling and how much—providing crucial early information about events ranging from flash floods to blizzards. And the network is especially irreplaceable when it comes to spotting tornadoes; it has substantially lengthened warning times and reduced deaths. Doppler radar has 'really revolutionized how we've been able to issue warnings,' says Ryan Hanrahan, chief meteorologist of the NBC Connecticut StormTracker team.
But now meteorologists and emergency managers are increasingly worried about what might happen if any of these radars go offline, whether because of cuts to the NWS made by the Trump administration or threats from groups that espouse conspiracy theories about the radars being used to control the weather. 'Losing radar capabilities would 'take us back in time by four decades,' says Jana Houser, a tornado researcher at the Ohio State University. If they go down, 'there's no way we're going to be effective at storm warnings.'
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
How Doppler radars work
The NWS installations form a network called the Next Generation Weather Radar, or NEXRAD. Inside each giant white sphere is a device that looks like a larger version of a home satellite TV dish, with a transmitter that emits pulses in the microwave region of the electromagnetic spectrum. Those pulses bounce off raindrops, snowflakes, hailstones—what meteorologists collectively call hydrometeors—and back to the dish antenna. (The pulses also sometimes bounce off bats, birds and even moving trains, which yield characteristic radar patterns that experts can usually identify.)
The power of the returning signals lets experts create a picture of size, shape and intensity of any precipitation—and this is what you see on a phone app's radar map or a TV broadcast.
But NEXRAD can do much, much more than show how hard it's raining. Within its sphere, each unit rotates and scans up and down through the sky, helping forecasters see what is happening at multiple levels of a storm system. These vertical profiles can show, for example, whether a tornado is forming or a storm is creating a downburst—a rapid downward blast of wind. 'Doppler radar basically allows us to see in the clouds,' Hanrahan says.
And then there's the 'Doppler' part itself. The name refers to a phenomenon that's familiar to many, thanks to the electromagnetic waves' acoustic counterpart. We've all experienced this, often most obviously when we hear an emergency vehicle siren pass nearby: the pitch increases as the car gets closer and decreases as it moves away. Similarly, the returning radar bounce from a rain droplet or piece of tornadic debris that is moving toward the emitter will have a shorter wavelength than the pulse that was sent out, and the signal from an object moving away from the radar will have a longer wavelength. This allows the radar to efficiently distinguish the tight circulation of a tornado.
The nation's radar system was upgraded in 2012 to include what is called dual polarization. This means the signal has both vertically and horizontally oriented wavelengths, providing information about precipitation in more than one dimension. 'A drizzle droplet is almost perfectly spherical, so it returns the same amount of power in the horizontal and in the vertical,' Hanrahan says, whereas giant drops look almost like 'hamburger buns' and so send back more power in the horizontal than the vertical.
Are Doppler radars dangerous? Can they affect the weather?
Doppler radars do not pose any danger to people, wildlife or structures—and they cannot affect the weather.
Along the electromagnetic spectrum, it is the portions with shorter wavelengths such as gamma rays and ultraviolet radiation that can readily damage the human body—because their wavelengths are the right size to interact with and damage DNA or our cells. Doppler radars emit pulses in wavelengths about the size of a baseball.
Being hit by extremely concentrated microwave radiation could be harmful; this is why microwave ovens have mesh screens that keep the rays from escaping. Similarly, you wouldn't want to stand directly in front of a radar microwave beam. Military radar technicians found this out years ago when working on radars under operation, University of California, Los Angeles, climate scientist Daniel Swain said during one of his regular YouTube talks. They 'had experiences like the candy bar in their pocket instantly melting and then feeling their skin getting really hot,' he said.
Similar to how a microwave oven works, when the microwave signal from a radar hits a hydrometeor, the water molecules vibrate and so generate heat because of friction and reradiate some of the received energy, says Cynthia Fay, who serves as a focal point for the National Weather Service's Radar Operations Center. But 'microwave radiation is really not very powerful, and the whole point is that if you stand more than a couple dozen feet away from the dome it's not even really going to affect your body, let alone the global atmosphere,' Swain adds.
At the radar's antenna, the average power is about 23.5 megawatts (MW) of energy, Fay says. (A weak or moderate thunderstorm may generate about 18 MW in about an hour.) But the energy from the radar signal dissipates very rapidly with distance: at just one kilometer from the radar, the power is 0.0000019 MW, and at the radar's maximum range of 460 kilometers, it is 8.8 x 10 –12 MW, Fay says. 'Once you're miles away, it's just really not a dangerous amount' of energy, Swain said in his video.
And Doppler radars spend most of their time listening for returns. According to the NWS, for every hour of operation, a radar may spend as little as seven seconds sending out pulses.
The idea that Doppler radar can control or affect the weather is 'a long-standing conspiracy [theory] that has existed really for decades but has kind of accelerated in recent years,' Swain said in his video. It has resurfaced recently with threats to the National Oceanic and Atmospheric Administration radar system from an antigovernment militia group, as first reported by CNN. The Washington Post reported that the group's founder said that its members were carrying out ' attack simulations ' on sites in order to later destroy the radars,—which the group believes are 'weather weapons,' according to an internal NOAA e-mail. NOAA has advised radar technicians at the NWS's offices to exercise caution and work in teams when going out to service radars—and to notify local law enforcement of any suspicious activity.
'NOAA is aware of recent threats against NEXRAD weather radar sites and is working with local and other authorities in monitoring the situation closely,' wrote a NWS spokesperson in response to a request for comment from Scientific American.
What happens if weather radars go offline?
NOAA's radars have been on duty for 24 hours a day, seven days a week and 365 days a year since 1988 (with brief downtimes for maintenance and upgrades). 'It's amazing what workhorses these radars have been,' Hanrahan says.
But they do require that periodic maintenance because of all the large moving parts needed to operate them. And with Trump administration cuts to NOAA staffing and freezes on some spending, 'we just got rid of a lot of the radar maintenance technicians, and we got rid of the budget to repair a lot of these sites,' Swain said in his video. 'Most of these are functioning fine right now. The question is: What happens once they go down, once they need a repair?'
It is this outage possibility that most worries weather experts, particularly if the breakdowns occur during any kind of severe weather. 'Radars are key instruments in issuing tornado warnings,' the Ohio State University's Houser says. 'If a radar goes down, we're basically down as to what the larger picture is.'
And for much of the country—particularly in the West—there is little to no overlap in the areas that each radar covers, meaning other sites would not be able to step in if a neighboring radar is out. Hanrahan says the information provided by the radars is irreplaceable, and the 2012 upgrades mean 'we don't even need to have eyes on a tornado now to know that it's happening. It's something that I think we take for granted now.'