Here’s a clip below from Tom Skilling’s post on the ChicagoWeatherCenter blog.
You’ve said that humid air is less dense than dry air. A recent article states pitchers like high humidity. Is that contradictory?
Thanks, David Labotka
Not really. With all factors equal, moist air is less dense than dry air because water (18) has a lower molecular weight than nitrogen (28) and oxygen (32).
Since lower air density offers less resistance to the flight of a baseball, the ball will travel farther when humidity is higher—advantage hitter.
However, when it’s humid out, a baseball absorbs moisture making it less bouncy which translates to about a three foot decrease in travel for each 10 percent increase in humidity.
Additionally a moist ball gives pitchers a better grip resulting in more ball spin—advantage pitcher.
The number of home runs hit in Denver has decreased since the Colorado Rockies began storing their baseballs in a humidor back in 2002.