As the US Open ramps up this week, most spectators will be focused on the tennis courts as athletes battle for triumph and glory. But behind the scenes, a handful of tournament organizers are watching the sky for a different kind of drama: signs of rain that could force a challenging decision. Should they close the stadium roofs?

The option to put a roof over the US Open is relatively new: Arthur Ashe Stadium — one of the tournament’s main show-courts the US Tennis Association’s National Tennis Center in Queens, New York — was retrofitted with a retractable roof in 2016. A second facility, the Louis Armstrong stadium, was rebuilt with a retractable roof in 2018.

The roofs were installed to prevent disruption and delays during inclement weather, says David Brewer, US Open tournament director. But weather prediction is full of uncertainty, and so is the decision about whether to close the roofs.

Every day of the tournament, Brewer says, he consults with a team that includes engineers and meteorologists about the probability for precipitation. They try to keep the roofs open as much as possible in order to keep play consistent for all players, while also preserving the historical spirit of an open-air tournament. But if they have to close the roofs, they want to make the call at the right time. It takes five minutes for the roofs to close, and even a sprinkle can make a hard court slick.

“Ideally, we are timing it in such a way that we are closing the roofs just a few minutes before the rain arrives,” says Brewer. “So, the players have a very brief break sitting on the court waiting for the roof to close. When it closes, they [resume] play and the spectators are none the wiser in terms of when the rain started.”

It was a sunny, 73-degree day when American tennis player Arthur Ashe won the first modern U.S. Open on September 9, 1968. In the decades that followed, the tournament experienced a string of “spectacular weather,” Brewer says. He started working at the USTA in 1997, when the organization was planning to build Arthur Ashe stadium. In the 20 years prior, there had been maybe two sessions rained out in all the US Opens combined. Because stormy weather had been so rare, the USTA opted not to put a roof on the stadium. It just didn’t seem necessary.

Then, in the early 2000s, rain struck — again and again. Five years in a row, Brewer says, the tournament ended on a Monday, a day later than planned, because of rain delays. Eventually, he says, “we asked our architects who designed Arthur Ashe Stadium to go back and see what we could do to put a roof on it.”

Their solution was a free-standing roof, supported by steel columns that are unattached to the stadium. Designed by Detroit-based architecture firm ROSETTI, the stadium cost about $150-million to build. According to ROSETTI, it is the largest retractable roof covering a tennis stadium in the world.

Ever since the Arthur Ashe roof was inaugurated in 2016, the USTA has consulted with private weather companies about when and whether to close it. At first, they worked with Meteo France, a French company with a division that specializes in sporting events. This year, they are working with ClimaCell, which says it uses high-resolution models to provide minute-by-minute, venue-specific forecasts for a variety of industries.

At least two specialists from ClimaCell are on site during the US Open. They sit in a room just a door away from the tournament control center, where Brewer and colleagues monitor matches and conditions. When a storm system appears to be brewing, he says, ClimaCell sends a couple extra people to help monitor video screens and produce forecasts.

Even with proprietary weather models and dedicated meteorologists giving live updates, the ultimate decision remains a guessing game. The wrong call can lead to further delays.

“We've had a couple of instances where we waited just a little bit too long, and the court got a bit wet, and we had to wait a few more minutes before play could resume,” says Brewer. Last year, rain fell on one side of campus and not the other, so the Arthur Ashe roof was closed even though it didn’t need to be. “We’re always guessing just a little bit right at the edge of when the precipitation is coming.”

The Ashe roof has been closed three or four times each year since 2016 and the Armstrong roof was shut twice last summer, Brewer estimates.

The roofs have generated some controversy, including criticisms that the structure of the Ashe stadium roof stifles air circulation and leads to suffocating heat. In response, Brewer says, the USTA has added some new cooling strategies this year — including personalized air-conditioning units for the players on the court.

What the weather will deliver to tennis tournaments of the future remains uncertain, says David Robinson, New Jersey’s state climatologist, who is based at Rutgers University in Piscataway, New Jersey.

Climate change is likely to make weather during the tournament warmer overall, a trend that has already begun. Since the 1980s, Robinson says, records show that average August temperatures in New York City have increased by one to two degrees Fahrenheit. Daily lows have increased slightly more than daily highs, with plenty of year-to-year variability.

But precipitation has, so far, shown no significant trend in either direction. The five years of rain that followed 20 dry years was “dumb misfortune or dumb luck,” says Robinson. “There is no trend where suddenly in the last five years it's raining more in the last two weeks of August, the first week of September.”

“It's just the luck of the draw, just like, in some respects, the Open is.”

Retractable roofs are far from the only innovations you'll find at the US Open this year. IBM and the US Open have worked together for over 25 years to bring new technological experiences to visitors and players alike. Find out more here.