Weather forecaster Chad Gimmestad leans toward an oversized computer screen to jab at double-digit rainfall totals. These data were recorded by volunteers who braved Hurricane Milton’s 55 mph gusts to read plastic rain gauges mounted in waterlogged central Florida backyards.

“I’m really surprised so many people had reports today,” says the National Weather Service meteorologist based in Boulder, Colorado. “This is their most important observation—maybe of their whole time volunteering—and so they want to get it right.”

At 7 a.m. on Oct. 10, in the chaotic hours after the record-breaking storm swept ashore, one citizen scientist in Daytona Beach Shores reported 15.8 inches of rain. Another near Lake Helen clocked 15.37 inches for a similar 24-hour period, and added in the notes section: “Lots of tree limbs down. Some roads are flooded due to lakes overflowing their banks.”

Observations like these are added to an internet database at 7 a.m. each day by volunteers with the nationwide Community Collaborative Rain, Hail & Snow Network, or CoCoRaHS. The observations from 26,500 stations across the country contribute to National Weather Service flood warnings that may save lives by accounting for the variability of how much rain fell and where. Radar and satellites are not sophisticated enough to provide such down-to-the-backyard estimates.

In one such alert, for the St. Johns River in Florida’s Seminole County, forecasters more than an hour’s drive away, in the city of Melbourne, added CoCoRaHS rainfall totals to other on-the-ground observations, radar data, and river models. They estimated that runoff from Milton could cause the river to rise to 10.2 feet by the night of Oct. 14.

“The river is forecast to reach Minor Flood Stage later tonight, and will continue to climb through Moderate Flood, reaching Major Flood Stage later this weekend,” reads the alert Gimmestad pulls up on his screen. It cautioned many roads were “impassable, limiting access to homes.”

CoCoRaHS reports also help forecasters provide tornado, hail, fire, and other weather-related warnings in real time by allowing participants to log storm notes in the network’s computer system any time of day.

These observations—which provide input in up to half of such warnings—get routed to the nearest National Weather Service station, where they ring alarm bells. Meteorologists use them to caution people to take shelter or evacuate. Scientists also use CoCoRaHS data after storms have passed to refine computer models to better reflect precipitation variability.

Such life-saving weather data are vital as the United States suffered 28 climate and weather disasters whose costs exceeded $1 billion each—the most such events ever recorded in a year. Storm warnings will become all the more important as a warmer atmosphere traps more moisture—leading to more recurrent and intense rainfall.

The Heritage Foundation’s Project 2025 calls for a breakup of the National Oceanic and Atmospheric Administration, which houses the National Weather Service, saying that these federal agencies push climate propaganda. But shutting down these essential services could stymie the ability of forecasters to issue comprehensive weather warnings and protect people at risk during climate disasters. 

As the presidential election looms and global warming intensifies, CoCoRaHS precipitation records, which account for two-thirds of the observational data collected by federal agencies on how much it rained or snowed, are becoming even more indispensable. 

“It’s a huge value,” he adds. “Radar is really good at capturing the pattern, and CoCoRaHS observations give us the amounts, and so we put those together and it gives us a really nice map of how much it rained, hailed, or snowed.” 

The Critical Role of Data Collection

Altogether, CoCoRaHS’s stations span all 50 states, Canada, the Bahamas, and several U.S. territories. The network comprises about 75 million measurements and growing. 

The effort emerged in the wake of a deadly 1998 flash flood in Fort Collins, Colorado, that caught many people by surprise. The network is now one among hundreds of citizen science projects nationwide whose data are helping researchers discover new drugs, identify new galaxies, and catalog species recovery.

“CoCoRaHS changed the way we do weather forecasting,” says Ellen McCallie, program director in the Directorate for STEM Education at the U.S. National Science Foundation. The consistency and reliability of the data are helping improve National Weather Service precipitation predictions, she adds.

After CoCoRaHS volunteers watch a training video, they are assigned a station number. They install a National Weather Service–approved cylindrical plastic rain gauge, from which they measure precipitation and record the data online.

Network coordinators, who often work for state climate offices, urge volunteers to collect readings each morning, even if there’s no precipitation. These data are immediately visible on weather service maps. Each station is represented by a dot whose color reflects the amount of precipitation—red for more, blue for less. 

In addition to the vast public benefit CoCoRaHS provides, the citizen scientists who are the backbone of the network say they benefit personally from the work, too.

“It’s something to do every day at 7 a.m.,” says Noah Newman, the program’s education and outreach coordinator. “One volunteer working their way through Alcoholics Anonymous got their five-year [sobriety] chip thanks to CoCoRaHS, because they said no to going to the bars so they could get up to read their rain gauge.”         

Retired Montana State University scientist and faculty member Bill Locke recounted in an email how recording daily precipitation in the CoCoRaHS database has helped him cope with his depression in the 11 years since he signed on to be a part of the network. 

“From now until March I need to pull on Bean boots, a headlamp, and appropriate attire to trek to my gauge,” he wrote, adding that the plastic cylinder is about 82 feet away from his Montana home. In the winter, these duties often involve measuring and collecting snow from a board on the ground and swapping cylinders if the existing one is full. “It’s tough to go back to bed after all that!”

A People’s Climate Record

The CoCoRaHS network isn’t the only example of how citizen scientists contribute to the nation’s climate record. Federal agencies also rely on about 8,700 people who volunteer with the 134-year-old Cooperative Observer Program, or COOP.

These citizens collect temperature and precipitation data daily from National Weather Service equipment, and then report it electronically to the service. This on-the-ground grassroots system is smaller and not as geographically diverse as CoCoRaHS, says meteorologist Gimmestad.

“Instead of having official weather reporting stations that are 30 or 40 miles apart—so we might have one per county—with CoCoRaHS, we might have 10 or 50 stations in the county,” he says. “This way, we don’t have to use one point to represent a huge area, and so we know how rainfall was distributed around that county.”

Data from CoCoRaHS and COOP—together with observations from weather stations at the nation’s airports—account for about 80% of the precipitation numbers that federal scientists use to compile what’s known as the U.S. Climate Normals—a catalog of temperature and precipitation averages from 1991 to 2020. The 30-year retrospective is vital for the health of the nation’s economy because it’s a go-to resource for businesses. 

“The construction industry wants to know how many rainy days there will be at a location in which they are putting in a bid—and to learn how to design air conditioning and heating for buildings,” says Michael Palecki, the lead scientist on the project at the National Centers for Environmental Information. “People want to know what the weather is going to be like where they are looking to move, and, of course, agriculture is one of our biggest users.”

Tracking Hurricane Helene

Some 11 CoCoRaHS volunteers work in Palecki’s office in Asheville, North Carolina. The physical scientist, who had to remove a few trees from his property following Hurricane Helene, recounts how the region spent two weeks without power and remains without drinkable tap water.

When the air conditioning went down in the National Centers for Environmental Information’s computer room—a vast repository of weather data—temperatures soared to 120 degrees, requiring officials to shut down the system and delaying the publication of weather-related information nationwide.

The life-saving value of volunteer precipitation data was also evident in North Carolina as hardy CoCoRaHS participants tugged on rain gear to collect rainfall totals from their plastic gauges in the face of Helene’s “biblical devastation.”

One wrote in observation notes from Flat Springs on Sept. 28: “Absolutely catastrophic impacts from flooding, landslides, and high winds. Major roads impassable. Neighboring fire department … completely carried away by Elk River.”

The North Carolina State Climate Office relied in part on CoCoRaHS observations to determine where, and how much, rain fell. Four network volunteers in the western part of the state recorded totals from Sept. 25 to Sept. 27: 24.12 inches in Spruce Pine, 22.36 inches in Foscoe, and about 22 inches each at stations south of Black Mountain and Hendersonville.

Using a federal weather atlas that categorizes the likelihood of extreme storm events, state weather officials determined rainfall produced by Helene likely qualifies it as a one-in-1,000-year storm.

“Yet another event of this magnitude within the state offers even more evidence that our climate is changing, and in extreme ways,” wrote Corey Davis, an assistant state climatologist, in an online summary of Helene’s formation and impacts.

Davis continued: “The rapid intensification of Helene over the Gulf, the amount of moisture available in its surrounding environment, and its manifestation as locally heavy—and in some cases, historically unheard of—rainfall amounts are all known side effects of a warmer atmosphere.”

The National Weather Service is currently updating this atlas, and in doing so, is relying “very extensively” on extreme precipitation data recorded by CoCoRaHS volunteers to determine where heavy rainfall was distributed over time, Palecki says.  

Understanding Science in Daily Life

One volunteer whose data will likely be reflected in this record is Matt Kelsch, a hydrometeorologist in Colorado who is also the Boulder County coordinator for CoCoRaHS. Kelsch has collected precipitation data for the network—or asked a house sitter to do it—without missing a day since June 2001.

His plastic rain gauge sits in his expansive backyard near his garden, which, on Oct. 10, is bone dry.

But it’s not always this way. Kelsch, who has an encyclopedic memory for notable water-related weather events, says the wettest year he recorded was 2013, when about 34 inches fell. And one of the “most impressive spells of snow” occurred in 2006, with 26 inches around Dec. 21, then 14 inches a week later, and 11 more inches seven days after that. 

For Kelsch, the value of CoCoRaHS lies in its ability to teach people of all ages to tune into the variability of precipitation in their own neighborhoods. Volunteering helps participants “improve their skills at estimating how much rain is falling,” he says.

“They can see when the storm is analyzed how much rain fell—their report was one of the dots that was used,” he adds. “CoCoRaHS, even though it’s simple, connects people with the science.”