Editor’s note: Stephen is a life-long Houstonian and avid weather-geek. He grew up fascinated with the wild Houston weather and loves writing about the processes that create it and its impacts on the area. You can find him on twitter @stephenuzick
By STEPHEN UZICK
Earlier this week I stumbled across an article highlighting how executives from an anonymous MLB team have 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 did not disclose how exactly they would be using the data, but based on the information requested it is safe to assume the team is looking at factors beyond the usual suspects of 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 – air density. Air density is basically a measure of how many air molecules are present in a given area. Lower air density means fewer molecules are present to cause friction on a flying baseball – a plus for hitters but not as beneficial for pitchers who rely on breaking balls.
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, despite the fact that 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.
Knowing what kind of temperatures and humidity levels to expect at certain stadiums can help teams make tweaks to their hitting and pitching strategy. Cooler or drier conditions can lead to a little more movement on breaking pitches due to increased friction, while hot and humid weather can give 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 this year, the heat and humidity are probably bigger assets than they may have been in years prior. So on those hot and muggy summer nights perhaps the Astros should open up the juice box and let the dingers fly.