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Rules of the roof: When to close and why

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The new $150 million retractable roof debuts at this year’s US Open, putting an end to lengthy rain delays inside the biggest stadium in Grand Slam tennis.

And while fans look up and marvel at the giant structure closing above them, there’s actually a whole team behind the scenes making sure the process runs smoothly from start to finish.

Two meteorologists from MeteoFrance Sport will be on site every day, monitoring weather conditions and providing updates to tournament referee Brian Earley every 30 minutes.

The first update will come each morning at 9 a.m., two hours before the start of play, as part of the tournament staff’s daily meeting, which includes Earley, tournament director David Brewer, USTA Billie Jean King National Tennis Center chief operating officer Danny Zausner, senior director of capital projects and engineering Chuck Jettmar and a Grand Slam supervisor.

This team will discuss the overall outlook for the day, with the forecasts drawing on extensive sporting experience from the world of tennis, soccer, auto racing and sailing to highlight any potential pockets of inclement weather.

Meteorologists Guy Bottlaender and Pierre-Yves Guillerm from MeteoFrance Sport track many environmental factors, including the location, height, density and speed of rain clouds, air temperature, humidity and wind speed. They then plot these data points into a model to accurately predict the forecast.

From there, the tournament referee will remain in constant communication throughout the day until the last ball is hit each night.

Brewer said the US Open is still an outdoor event and, as such, the roof will be kept open as much as possible unless rain or the threat of rain necessitates closure. He said decisions will largely be made proactively rather than retroactively, using the forecasts to help formulate plans. Should rain be imminent, a series of steps will ensure disruptions are kept to a minimum.

The final decision on when to close the roof ultimately comes to tournament referee Earley, whose decision is final. In anticipation of inclement weather, he may order the stadium to be pre-conditioned, asking operators closing the shutters around the upper bowl and activating the air management system.

The meteorologists have dedicated phone and walkie-talkie lines directly to the tournament scheduling office. Once they advise that rain is on its way, the roof operators – located in a room on the broadcast level overlooking the court – are put on standby, and workers in the chiller plant which handles the air system are notified.

At the next available stoppage in play, either a change of ends or a set break, Earley will go onto the court to notify the players. At that point, the message is sent to the control room to begin closing the roof. If the shutter doors that surround the upper bowl of the stadium were not previously closed and if the air management system not already activated as part of the pre-conditioning process, these are also set in motion. Additionally, all doors leading from the concourse areas to the Club and Promenade levels will be closed.

The roof can close in fewer than seven minutes and the shutters can close in 30 seconds. The time it takes to establish a given temperature and humidity in the stadium depends on the current atmospheric conditions.

Once the roof has closed and the weather-tight seal has activated, air will be circulated around the stadium to maintain a similar temperature and humidity as it was prior to the roof closing.

Vents running around the upper bowl determine the flow of air, with laser-focused vents shooting air to the lower bowl and two other sets of vents pushing air to the upper deck. It’s important to keep the stadium at specific temperatures and humidity ranges to stop condensation forming on the inside of the roof.

A decision will also be made whether to turn the stadium lights on, if they weren’t already. The power of the lights will be dictated by the ambient light in the stadium.

The roof will be either fully open or fully closed and it will not be used to protect ticket holders from heat or direct sunlight. The position of the roof for succeeding matches will be determined by the tournament referee.

Three workers in the roof control booth follow progress through a number of computers, cameras and infrared sensors to monitor everything from roof speed and braking systems to temperature, dew point and humidity. The roof can open and close during winds up to 45 mph.

The players, who will be informed about the status of the roof and the forecast for the match before each match, will stay on the court while the roof is closed. Some players may take the opportunity to take a bathroom break, but they won’t be instructed to return to the locker room. By being preemptive, tournament officials hope there won’t be a situation where players have to leave the court, wait for it to be dried and then return for a warm-up before resuming play.

Meteorologists remain on site until the last ball is hit and roof operators are available in the stadium 24 hours a day throughout the duration of the tournament. Workers also man the chiller plant outside the stadium at all times.

Organizers expect to preemptively close the roof overnight in preparation for rain before the next day’s first matches at 11 a.m. Other decisions will be made in real time utilizing the micro forecasts from the weather forecasting team, which utilizes a dedicated radar in Brooklyn to monitor local conditions.

Flushing Meadows has its own micro climate created by its proximity to the ocean to the east and to built-up Manhattan to the west, both of which impact the local conditions.

For example, just because there’s a 70 percent chance of rain in New York City, there might only be a 50 percent chance in Queens. Even then, a light, quick shower could bypass the tennis center completely, even if other parts of Queens get rain. But even if mother nature does threaten to interupt play, the show will go on inside the grandest tennis stadiumon the globe.