Home run weather
Traditional baseball wisdom says that pitchers are “ahead of the hitters” when the season starts in the chilly early spring, while on the hot days of summer, scoring—and home runs—soar. There is a real, scientific reason for that phenomenon, says PopularScience.com: Struck baseballs fly farther on the hot, humid days of summer. Heat causes gases to expand, which reduces air density, or the number of molecules packed into one space. As a result, baseballs face less resistance as they fly through the air on a hot day. “For a ball hit at the typical home run speed and trajectory, a 10 degree [Fahrenheit] change in temperature is worth about a little over 3 feet in distance,” says physics professor Alan Nathan. Altitude and humidity also affect the flight of a baseball. Humid air holds more water vapor, which displaces heavier gases, like nitrogen and oxygen. The resulting reduction in air density allows batters to knock ’em out of the park more easily. Air density is also lower at higher altitudes, which is why Coors Field, the mile-high home of the Colorado Rockies, is known as a hitter’s heaven and a pitcher’s worst nightmare. Nathan says wind can have the most pronounced effect of all: Even a 5 mph wind blowing toward the outfield can carry a fly ball an extra 20 feet—the difference between an out and a dinger.