Turns out that the have one of the worlds experts on
the physics of baseball, Prof. Al Nathan, in our department. We asked
him your question, and his answer is:
"The main effect with
temperature, assuming constant humidity, is the air drag. Higher
temperature means lower air density which means less drag. I have not
tried to calculate this for a softball, but for a baseball, an extra 10
degrees F in temperature might be worth about 4'-5' on a long fly ball.
The effect might be larger for a softball because drag plays a
larger role (due to the larger area). I have not done that calculation,
although it is not hard to do.
So, the answer to the question is ...Yes, higher temperature means (slightly) longer distance."
(published on 10/22/2007)