Recently I stumbled across an article highlighting how executives from an anonymous MLB team reached out to NOAA’s National Centers for Environmental Information to request weather data for all of the cities in which they play.  Given the importance that has been placed on analytics in this era of sports, it should come as no surprise that teams are looking to factors beyond the playing field and thinking outside of the box in attempts to gain any possible advantage.  

This un-named team (but let's be honest, there’s a very good chance it is the Astros) did not disclose exactly how they would be using the data, but based on the information requested it is safe to assume the team is looking at factors beyond just wind and rain.  More than likely these club executives are also taking account of temperature and humidity conditions at each ballpark. Both of these factors share one commonality which affects the flight of a baseball off the bat and out of a pitcher's hand - air density. On a very basic level air density is a measure of how many air molecules are present in a given area.  

As the temperature warms air molecules begin to move faster causing the air to expand. This expansion leads to more space in between the molecules which in turn lowers air density.  Humid air is also less dense, even though most people describe the air as feeling heavy when it is muggy out. The lower density is due to the fact that water molecules are actually smaller than the nitrogen and oxygen molecules that make up the majority of the air we breathe.  When the air is more saturated (humid) water molecules displace more of those larger molecules creating a less dense air mass (Nerd moment – this is the same reason humid air rises to create storms).

Knowing what kind of temperatures and humidity levels to expect at certain stadiums can help teams make tweaks to their hitting and pitching strategy.  In cooler or drier conditions the air is more dense which can lead to a little more movement on breaking pitches due to increased friction, while in hot and humid weather, or at high altitude like in Denver, the air is less dense giving fly balls a bit more oomph towards the fences.

In Houston we have an abundance of heat and humidity for 99% of baseball season which is part of the reason Minute Maid was built with the retractable roof.  Although the overall effect of air density is rather small - when combined with the Astros’ ball-mashing lineup and short outfield corners, the heat and humidity are assets not to be discounted for the home team. So on those hot and muggy summer nights perhaps the Astros should open up the juice box and let the dingers fly.