A look at the weather's effect on baseball
Stephen Strasburg's first pitch as a Washington National? A 97 mph fastball. The fastest pitch of his June 8 Nationals debut? 101 mph. Just how good was Strasburg? He had a franchise-record 14 strikeouts in his first major league start, and his change-up was faster than some pitchers' fastballs.
Is there anything that can slow down a Strasburg pitch? A strong gust of wind could. But it could also speed it up. How does the wind's effect on pitchers -- and on batters and fielders -- compare to that of temperature, pressure and other weather factors? Let's take a look...
Rain or snow have the most obvious potential impacts on a ballgame, ranging from a sloppy field or pitching mound (though mounds can have issues even on perfectly nice days, as Strasburg recently found out) to delay or postponement of the game. Other elements of the weather can have more subtle but sometimes significant effects.
The wind's effect on a pitched ball is fairly small, mainly because the ball is moving so fast over a relatively short distance. For example, meteorologist Jan Null calculates that a ball thrown at 90 mph into a 10 mph wind would slow ever-so-slightly to about 89.3 mph. A 10 mph wind at its back would increase the ball's speed to about 90.7 mph. And a cross-wind can blow a fastball off track by about three inches. The faster the pitch, the less vulnerable it is to the wind.
Wind has a much greater effect on fly balls, which travel a much greater distance than pitched balls, and if hit high enough can get caught up in stronger winds higher up in the air.
According to Keith Heidorn, a.k.a. The Weather Doctor, a baseball that travels 400 feet with calm winds would go about 445 feet with a 15 mph breeze behind it, all other factors being equal. Conversely, a wind blowing in from the outfield can be the reason a well hit ball stays in the park, while a cross-wind can be the difference between a fair or foul ball.
Note that the architecture of a stadium can often create winds that are different (in direction and speed) than the environment outside the park. Swirling stadium winds have been known to play havoc with really high pop-flys, frustrating the fielders trying to catch them.
Temperature and pressure
First, there's the general discomfort caused by unusually cold weather, which can negatively impact pitchers and batters alike. Major League Baseball rule 8.02(a) allows umpires to permit pitchers to blow on their hands to keep them warm in cold-weather games, provided the manager of each team agrees. Chris Constancio at The Hardball Times found that cold weather leads to both more strikeouts and more walks. The latter may be due to the ball being harder to grip in the cold and, therefore, more difficult to control.
The most pronounced effect of temperature, and pressure, is probably on fly balls. Temperature and pressure are related to the density of the air, which can significantly affect how far a ball flies.
As the temperature increases, air molecules bounce around more actively, which expands the air and lowers its density. Air is 12 percent less dense at 95 degrees than at 30 degrees, according to Exploratorium. Constancio found that more than 4 percent of batted balls go for home runs when the temperature is 75 degrees or warmer, but that rate drops to near 3 percent in unusually cold weather.
Meanwhile, decreasing pressure (which is just the weight of the air above) also has the effect of expanding the air and spreading out its molecules, thus making the air less dense. This is why baseballs carry so well at Coors Field in Denver, where the high elevation (about a mile above sea level) means lower air pressure -- pressure decreases about 3-4 percent for every 1,000 feet in altitude. Fluctuations in pressure brought by day-to-day weather can also help or hurt the flight of a ball, though not nearly as much as those due to altitude.
Since we typically think of humid air as being "thick" -- "you can cut the air with a knife," the saying goes -- it wouldn't be surprising if your assumption is that humid air is heavier than dry air. But it would be wrong.
Dry air and humid air actually have the same number of molecules, and it turns out the increased number of water molecules in humid air comes at the expense of nitrogen and oxygen molecules. In other words, as water molecules come into the air, nitrogen and oxygen molecules leave. The result? Humid air is actually less dense than dry air because water molecules (H2O) have a lower molecular weight than both nitrogen (N2) and Oxygen (O2) molecules.
So in theory, humid air would be considered more conducive to home run balls than dry air. In reality, though, the affect of humidity on air density is relatively small compared to that of temperature and pressure. In fact, the difference in air density between humid air and dry air (with all other factors being equal) is only about 1 percent, according to Exploratorium.
A couple of degrees, a few inches
It's clear the weather can influence a baseball game in a variety of ways to varying degrees. Is the impact as much as a pitcher having his mechanics right, or a batter being "in the zone"? Most of the time, probably not.
But just as we know in Washington that a degree or two can be the difference between a soaking rain or several inches of snow, there's every reason to believe that, from time to time, the weather can be the difference between strike three or ball four, or a home run instead of a long out. In a game of inches, Mother Nature does indeed have a say in who plays the role of hero... or goat.
Weather and Baseball (Jan Null on examiner.com)
Weather and Baseball (The Weather Doctor)
The Carry of a Fly Ball
Temperature Effects (The Hardball Times)
Science of Baseball (Exploratorium)
Understanding air density (USATODAY.com)