It’s 82 degrees with a healthy breeze as the sun sets behind the third base line at Coors Field. It is without a doubt a perfect day for baseball in Denver.
At the same time, roughly 500 miles east in Kansas City, Mo., the Royals are still waiting to play a game that was scheduled to start two hours ago. The rain is falling in sheets over the soaked tarp. It’s a bad day for baseball.
Since the 1870s, weather and baseball have been tied together by rainouts, snowouts and coldouts. Games have been played entirely in the rain, while others were not played because of forecasted rain that never came.
I have spent most of the past decade studying baseball weather, looking at the perfect weather in Denver and the storms in Kansas City through a different lens.
That breeze in Denver is a 14 mph sustained wind blowing out to left-center field, and combined with the above-average heat and elevation of Coors Field it makes for a hitter’s paradise. The storms in Kansas City will clear, but the damage has already been done. What started as a 98 degree day has cooled down to 71 degrees in the downpour. The 27-degree drop means a typical home run ball will lose about 10 feet of carry, oftentimes the difference between runs on the board and a warning-track out.
Weather matters in baseball in more ways than meet the eye. Wind, elevation, heat and humidity all have meaningful impacts on how far a ball carries and how many runs are likely to be scored.
On the surface, the impact of wind is fairly self-explanatory and is likely something most people already realize. If winds are blowing out from home plate to the outfield, that wind will literally help push the ball over the fence on a deep fly.
If winds are blowing in, it has the opposite effect. Certain parks are very wind-sensitive, and the results can be extreme. In Chicago’s Wrigley Field (see image below), a wind blowing out at 10 mph or greater increases home runs by approximately 50%, while a wind blowing in at less than 10 mph decreases home runs by 33%. That is a truly massive swing in outcomes and run expectancy based purely on wind orientation.
To make matters more interesting, each ballpark responds to wind a bit differently. Let’s use a similar wind as the Wrigley example and apply it to San Francisco’s Oracle Park (see image below). In this case, the result of an 11 mph wind blowing out represents only a 1% increase in home runs. This ballpark was specifically built to minimize wind impacts from this prevailing westerly flow (a wind blowing out), so the minimal impact is a plan, not a coincidence.
Each park has its own micro-climate, and knowing how each park is impacted by a wind of a particular direction and intensity can help to predict runs before the games even happen. All of the listed examples are from WeatherEdge, a tool built to pull weather data and statistics from past games, then use those numbers to project the scoring impact from weather of an upcoming game.
The higher up you are, the thinner the air gets, meaning less drag on the ball and thus better carry on a well-hit ball. Thinner air at elevation can also impact pitches themselves. With less air resistance on the ball, it’s harder to get a breaking ball to break. There’s a reason Coors Field is at or near the top of ballparks for run scoring every year. Breaking balls that don’t break and fly balls with extra carry makes a brutal combination for pitchers in Colorado.
Simply put: hot air is thin air, and cold air is dense air. The warmer it gets, the better it is for hitters, because the ball carries farther in hot, thin air. In the following examples at New York’s Yankee Stadium (see two images below), wind is not a significant factor in either example (just 4 mph in the first game, and blowing across the field in the second game), but the hitting conditions are very different. The first game was played in warm weather, and expected home runs jumped 14%. The second game was played in weather that was 35 degrees cooler, and the expected home run rate dropped 30%.
There’s a reason this is fourth on the list: it’s not as big of a factor as the others—but it still matters. Counter-intuitive as it is, humid air is actually less dense than dry air. We already know that less-dense air helps a well-hit ball travel farther, so that means that a hot humid day has some of the best hitting conditions out there.
It’s worth mentioning that dewpoints are a better measure of humidity than the classic relative humidity percentage. Dewpoints below 50 are dry, while those around 70 or higher are very humid. Below is a heat/humidity combo game at St. Louis’ Busch Stadium (see image below), another game where wind isn’t a significant factor at just 4 mph, but the high heat and humidity increased home runs by 20%.
Case Study: Texas Rangers
All of these various weather factors, especially when combined, can lead to dramatic boosts to run scoring. For proof of that look no farther than the Rangers, who are giving us a near perfect case study in just how much the weather really matters.
This year the Rangers are playing their first season in a new ballpark. It sits right next to the old park and has similar park dimensions. One notable difference between the two ballparks is that the new park has a retractable roof, and they have been closing that roof for the majority of games this season to negate the Texas heat.
The impact on scoring has been stunning. Last year Globe Life Park had the second highest total of runs scored per park, behind only Coors Field. Through mid-August this year the new park was 27th in that same metric. It’s still early, but the numbers are telling.
Weather matters in baseball, and not just the weather that cancels games.