Why so many Atlanta Braves rain delays? Science could explain.

Also: Why SunTrust Park planners didn’t take precipitation into consideration when building the stadium
SunTrust Park rain delays
A member of the grounds crew walks the edge of the tarp prior to a rain delay in the game between the Atlanta Braves and the Chicago Cubs at SunTrust Park.

Photo by Kevin C. Cox/Getty Images

The Braves-Cubs opening pitch was scheduled for 7:35 p.m., but the July 18 game didn’t get underway until 10:05 p.m. A storm materialized over SunTrust Park. The tarp was rolled out onto the field. It rained. It stopped. It rained again. It stopped again. The tarp was rolled up again. The tarp was rolled out again. Fans headed to the concession stands while families headed to the parking lot. SunTrust Park literally had a black cloud hanging over its head. Two and a half hours later, the tarps were pulled for the last time. By then, the Braves apparently were washed out and fell to the Chicago Cubs in a resounding 1-5 loss.

The Tuesday game was the 11th rain delay the Braves had experienced in their 46 games at SunTrust Park. That’s nearly 25 percent of home games. As Mother Nature continues to upset Atlanta fans of America’s favorite pastime, some are wondering: Why have there been so many rain delays at the new stadium? Well, after a recent University of North Carolina and University of Georgia study about rainfall patterns around Atlanta—we might have a clue.

“The city of Atlanta can sort of be a controlling mechanism for where thunderstorms are more likely to generate,” says Jordan McLeod, regional climatologist for the Southeast Regional Climate Center and lead author of the peer-reviewed study.

The short answer: On typical summer days, Atlanta can produce its own storms, many of which follow a predictable pattern and path. SunTrust Park happens to be in a part of the city that’s primed for extra rainfall.

The long answer: We’ll start with a concept called the urban heat island effect. Because Atlanta is fit for retaining heat with its large amounts of asphalt, concrete, and carbon emissions from cars, it’s typically a hot bed in comparison to its cooler rural surroundings. This provides one key element to fuel rainstorms: rising warm air surrounded by cooler air. Storms usually form as the city’s surfaces begin to cool and re-emit heat back into the atmosphere. This typically happens in the evening—right around the time of, say, the opening pitch of a baseball game.

However, where these rainstorms travel once they form depends on what the study calls the urban rainfall effect. Because winds typically blow from the south and west, storms produced by Atlanta’s heat island are more likely to be pushed downwind—east and north of the city. This focuses rainfall on the outskirts of the city—from I-285 outward, including north Fulton, east DeKalb, east Cobb, and Gwinnett counties. This would explain why Turner Field, which is in the heart of Atlanta, would receive less rainfall than SunTrust Park, which is just outside the perimeter. The study collected rainfall data from 14 summers between 2002 and 2015, a grand total of 1,285 days, and found the SunTrust Park area received some of the heaviest average rainfall throughout the metro region. Although the daily precipitation increase is marginal at hundredths of an inch, it’s significant considering the small region and long timeframe of the study.

Average daily precipitation in Atlanta summer
Mean daily precipitation in Atlanta and its metro areas during meteorological summers, from 2002-2015.

McLeod, J., et al., Spatio-temporal rainfall patterns around Atlanta, Georgia and possible relations..., Urban Climate (2017)

“People think that when we have these afternoon pop-up thunderstorms around Atlanta that they’re totally random,” says University of Georgia professor and former NASA scientist Marshall Shepherd. “But what our research has shown for many years is that they aren’t so randomized at all.”

Shepherd, who co-authored the study and has spent 20 years researching urban rainfall, was watching the Braves-Cubs game during the 2.5-hour rain delay. He pulled out his phone and checked the weather radar. There it was: a motionless storm dumping rain on SunTrust Park, and a model example of the study’s results. McLeod later determined the storm was fixed over the stadium because of weak, counteracting winds.

However, the study has a limited scope. It applies only to Atlanta’s typical summer days—muggy and sweltering with no major weather fronts—which is when microclimate factors can have the biggest effect.

“I would not go so far as to say, ‘our study conclusively is the reason why they’ve had more rain today,’” Shepherd says. “I would say our studies have shown that area [where SunTrust Park is] tends to receive relatively more rain than other parts of the Atlanta area.”

There is no doubting rain has become a thorn in the side of some Braves fans. So did SunTrust Park planners take precipitation into consideration when building the stadium?

“It was just not something that was part of our study or research that we did,” says Mike Plant, president of development for the Atlanta Braves. “We looked at 30 years of wind studies and sun studies. We’re not in a region of the country, we believe, that would justify spending time looking at precipitation. There’s just not an overabundance of precipitation.”

Rather than try to avoid inevitable rain, Plant said planners tried to mitigate the effect of delays. Architects more than doubled the size of the park’s canopy from what existed at Turner Field in order to block more seats from the rain and sun, and included larger concourses and entertainment areas such as the Battery to help pass the time. Planners entertained the idea of a retractable roof, but Plant says the concept got shelved quickly, and there’s little chance it’ll be considered again.

“We, universally, all feel really positive about the fact that we think baseball is best played outdoors,” Plant says. “We’re really happy with the decision to keep it an open-air venue.”

Plant explained that precipitation also wasn’t looked into because “there’s just no way to predict weather here,” saying the large number of rain delays has to do with this season being abnormally wet. Although this summer has been the 16th-wettest season in almost 150 years, Shepherd and McLeod disagree in saying rain is unpredictable.

“In the Atlanta area itself, sometimes the thunderstorms are not so random,” McLeod says. “I guess that’s one thing [this study] is trying to suggest.”

“This highlights the fact that city planners, organizations, and businesses need to consider the subtle nuances and patterns of weather around the city, because they’re not always all the same,” Shepherd says.