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Can weather predict home runs for your MLB team? The data says yes
It’s going, it’s going, it’s gone — or is it?
Some days a baseball jumps off the bat and never looks back. Other days, the same contact dies in the outfield air, landing short of the wall. And the difference may not always be in the power of the batter — but physics.
Across Major League Baseball, weather conditions like temperature, wind, humidity and atmospheric pressure can subtly change how far a baseball travels. Those shifts alter air density — the amount of resistance pushing against a moving ball — and even small changes can be enough to turn a warning-track flyout into a home run.
“In baseball, you’re playing the weather,” AccuWeather meteorologist Geoff Cornish said. “Hot day in Texas? Thinner air. The ball flies farther. Cold night in San Francisco? Heavy air — you won’t hit fly balls.”
More: Scientists weigh in on spike of home runs in MLB
How air density and elevation carry the ball
At the center of how weather affects home runs is air density — how tightly packed air molecules are in a given space. That density determines how much resistance, or drag, a baseball encounters as it moves through the air, Cornish said.
Air pressure is the main factor that sets that density. Higher pressure packs more air molecules into the same space, increasing the number of collisions with a baseball and slowing it down faster. Lower pressure means fewer molecules and less resistance, allowing the ball to retain more of its speed over distance.
Even small changes in that resistance can add up over the 350- to 450-foot flight of a ball.
Elevation is where those pressure differences become most obvious.
As altitude increases, atmospheric pressure drops because there is less air above the surface pushing downward. The result is thinner air and lower drag conditions, Cornish said.
Denver’s Coors Field, at about 5,200 feet above sea level, is the clearest example of that effect — and what Cornish calls “a hitters’ paradise.” In that environment, baseballs do not gain extra lift; they simply lose velocity more slowly after leaving the bat, which extends their flight.
“There’s no ballpark that’s even remotely close to Coors Field,” he said. “The next closest is Arizona, and that’s just over 1,000 feet. Then Atlanta is third highest. And they’re all hitters’ parks.”
Does humidity influence how far a ball travels?
Humidity affects baseball flight in ways that often run counter to intuition.
Moist air contains a higher proportion of water vapor, which is lighter than the nitrogen and oxygen that make up most of the atmosphere. When humidity increases, some heavier gas molecules are displaced by these lighter ones, slightly lowering overall air density. With fewer dense air molecules in the path of a moving baseball, aerodynamic drag decreases and the ball can carry marginally farther.
But humidity also affects the baseball itself, not just the air around it. Moisture can influence the leather and core, changing how the ball compresses at impact. It can also affect grip and spin, which in turn alters pitch movement and contact quality.
Because it influences both the environment and the ball’s physical behavior, humidity is more variable in its effects than temperature or pressure.
"Generally if it’s humid the ball will travel more," Cornish said. "But if the ball gets saturated, it’ll deaden the ball a little bit."
They can also become slightly heavier and less lively off the bat — which is one reason some ballparks and leagues use humidor systems to store baseballs under controlled conditions.
Those systems regulate temperature and humidity to keep balls closer to a baseline condition, often around 70 degrees and 50% humidity, helping reduce extremes in how the ball performs from game to game.
Does wind help or steal home runs?
It depends on the situation — and the stadium.
Wind is one of the most immediate and visible weather factors affecting how far a baseball travels because it changes the relative air the ball moves through. A wind blowing out toward the outfield reduces the effective airspeed against the ball, lowering drag and adding carry. A wind blowing in does the opposite, increasing resistance and knocking down fly balls that might otherwise leave the park.
“There are some ballparks more conducive to trouble because of wind,” Cornish said.
In Kansas City, for example, wind patterns frequently work against hitters. Even when wind is present, it more often suppresses home runs than boosts them, creating conditions that favor pitchers. Cornish said that effect may have more to do with stadium design and how airflow interacts with the structure than wind alone.
Meanwhile, in Chicago, the wind can swing outcomes on any given day. Even outside of the classic lake breeze setup, shifting wind direction and speed can turn the same contact into a routine fly-out or a home run.
“Wrigley Field is the token field where wind can make or break a deep fly ball,” Cornish said. “There will always be that lake breeze — even on a fair weather day.”
Unlike temperature or air pressure, wind is highly variable at the field level. It can change direction or intensity within short time frames, making it one of the least predictable factors in ball flight.
Because wind operates at both the broader atmospheric scale and the localized stadium level, it is often the factor players and fans notice most — even though, as Cornish notes, “statistically, it more frequently subtracts than adds to the distance hit."
Do baseballs travel farther on hot or cold days?
Temperature affects baseball flight by changing air density — how tightly packed air molecules are in a given space — Cornish said.
As temperatures rise, air molecules gain energy and move faster, which causes them to spread farther apart. That lowers air density and reduces the number of air molecules a baseball collides with as it travels through the air. With less resistance, or drag, the ball maintains more of its speed after contact.
That is why hot-weather games, particularly summer afternoons and nights in places like Texas, tend to produce more carry. The same swing that results in a routine flyout on a cool night can travel several feet farther in warmer air, sometimes enough to clear the wall.
“This is why there are more home runs in the middle of the summer than on the book ends,” Cornish said.
More: Cold weather is a quiet thief that steals your golf distance
How ballparks try to account for weather differences
Not all ballparks are designed to play the same way — and many are built specifically to offset the effects of weather and environment.
At Coors Field in Denver, the challenge is elevation. This is also why ballpark design in Denver historically accounted for altitude, Cornish said. Stadium dimensions and outfield spacing have been adjusted in part to balance the offensive advantage created by reduced air resistance, though the environment remains consistently hitter-friendly.
Other parks take the opposite approach by removing weather from the equation entirely. Domed stadiums, such as Rogers Centre in Toronto, are designed to create a controlled environment where temperature, wind and precipitation have minimal impact on play. By closing the roof, teams can eliminate many of the day-to-day atmospheric variables — including wind shifts and temperature swings — that influence ball flight in outdoor parks.
Rogers Centre, originally SkyDome, was the first enclosed stadium in baseball with a retractable roof. Several modern stadiums followed, allowing teams to adjust conditions depending on weather. In those cases, airflow, humidity and temperature can be partially stabilized, reducing the variability that comes with outdoor environments.
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Brandi D. Addison covers weather across the United States as the Weather Connect Reporter for the USA TODAY Network. She can be reached at baddison@gannett.com.Find her on Facebook here.
This article originally appeared on USA TODAY: Are more home runs in the forecast? Weather may be the reason
