Weather a key ­factor in baseball

While it’s wonderful that we have received plentiful precipitation this winter, like many in the Bay Area, I’m ready for warmer and dryer weather patterns.

Spring also means the beginning of baseball season, and I love hearing the ping of aluminum bats emanating from the ball fields near our house. As batters swing and connect with a pitch, I wonder how many are aware of how changes in weather conditions will affect the ball’s flight.

Travel distance and trajectory of any projectile can be mathematically predicted. Once a ball is sent in motion, it will continue to move unless acted upon by external forces like gravity or friction. The force of gravity is constant near the earth’s surface, but frictional forces vary.

Friction is the result of the resistance of the molecules in the air, commonly referred to as air density. Near the surface of the earth, air density changes are mainly due to variations in meteorological conditions.

Consider air temperature. Cool air has a slightly higher density than warm air. A batted ball struck hard enough to travel 350 feet during a 50 degree night game would travel approximately 365 feet during a 90 degree day game, about a 7 percent difference. This calculation assumes that there is no wind, and air pressure and relative humidity conditions are identical.

Calculating the effects of increasing relative humidity is a bit trickier. A common assumption is that moist air is heavier than dry air, and therefore, more dense. Actually, the opposite is true.

The molecular weights of nitrogen and oxygen, which make up 99 percent of our lower atmosphere, are 38 and 32 atomic units, respectively. Water vapor (H2O) only has a molecular weight of 18 atomic units. Increasing the humidity, which means adding water molecules to replace dry air molecules, actually results in less dense air.

Compared to temperature changes, the effect of increased relative humidity is slight. At a temperature of 70 degrees, a ball hit 350 feet will travel about one foot farther if the relative humidity is increased by 30 percent. If the air becomes extremely moist, the ball could absorb some of the moisture and gain weight, lessening the distance it will travel.

Change in atmospheric pressure can have a significant effect on the distance a batted ball travels. Air pressure decreases with elevation, so a good example is to compare the distance a ball will travel at a stadium located near sea level to one located in the mountains. A ball at sea level in the Oakland Coliseum that travels 350 feet would land about 25 feet farther in the mile-high city of Denver, assuming identical wind, temperature and humidity conditions.

All the weather-related effects of flight distances discussed here were calculated in still air. Winds are seldom calm, and even light winds can have a significant impact on the distance a ball travels. For example, a 5 mph wind blowing out to center field will carry a ball about 30 feet farther than a ball hit well enough to travel 350 feet in calm air.

So, bring on the warm dry spring weather and take me out to a ball game. It’s time to watch kids of all ages try to hit a ball into the air. But how far it will travel depends on the batter’s skill – and the weather.

Woody Whitlatch is a meteorologist retired from PG&E. Email your questions or comments to

Woody Whitlatch
Woody Whitlatch

Woody Whitlatch is a meteorologist retired from PG&E. Email your questions or comments to