Does Weather Affect Home Runs? What 133,420 Outdoor MLB Starts Show
Warm air carries the ball and wind blowing out turns fly balls into homers — everyone knows that, which is exactly why it is worth measuring. We matched four seasons of starts to their first-pitch weather and compared each game with what the same ballpark gives up in the same month.
Published September 2026 · 6 min read
1. The Data
133,420 starts by MLB batters in open-air games from April 2023 through September 25, 2026, regular season only, with the temperature and wind MLB records at first pitch. Domed and closed-roof games (29,074 more starts) are set aside — they homered at 11.7%, right on the league's 11.9%.
The raw comparison is misleading on its own. Cold games cluster in April and late September and in certain parks; hot games cluster in July and in others. So every table below carries an “expected” column: the home run rate of the same ballpark in the same month. The gap between the two columns is what weather adds on top of what you already knew from the schedule. The hitters in each band were near-identical in power, so the lineup is not driving it either.
2. Temperature: The Cold Matters More Than the Heat
| First-pitch temperature | Starts | Homered | Same park, same month |
|---|---|---|---|
| Under 55°F | 7,804 | 8.9% | 10.6% |
| 55–64°F | 19,676 | 10.5% | 10.9% |
| 65–74°F | 40,617 | 11.6% | 11.8% |
| 75–84°F | 47,915 | 12.7% | 12.3% |
| 85°F and up | 17,408 | 13.3% | 12.8% |
The raw spread is large: 8.9% below 55°F against 13.3% at 85°F and up. But most of it is the calendar and the ballpark. Against the same park in the same month, a cold game ran about 1.7 points low while a hot game ran only about half a point high. The physics is real in both directions; the betting-relevant part is lopsided. A raw April night in Chicago or Cleveland is a genuine home run suppressor. A hot July night is mostly already priced by the fact that it is July.
3. Wind: In Hurts, Out Barely Helps
| Wind at first pitch | Starts | Homered | Same ballpark |
|---|---|---|---|
| Blowing in, 10+ mph | 7,522 | 10.3% | 11.9% |
| Everything else | 108,836 | 12.0% | 11.9% |
| Blowing out, 10+ mph | 17,062 | 12.0% | 11.5% |
Wind blowing in at 10 mph or more cut home runs to 10.3% against 11.9% for the same ballparks — about 13% fewer. Wind blowing out at the same speed lifted them only about half a point above normal. Part of that is measurement: MLB records one wind reading at first pitch, at one height, and stadium walls swirl it. Part of it is where wind blows out: the parks that see it most often already play as hitter-friendly, so “wind out” is partly already in the park's number.
4. Wrigley Field Is the Exception
One park behaves the way the folklore says. At Wrigley Field, starters homered in 16.7% of games with wind blowing out at 10 mph or more (38 games), 12.5% in ordinary conditions (211 games), and 8.3% with wind blowing in (66 games). The samples are small, but a doubling from in to out is not noise. Open bowls on the lake see wind that stadium walls elsewhere break up. Park-specific effects like this one, and altitude at Coors Field, are where weather earns its keep.
5. When the Weather Is Actually Known
MLB publishes a game's first-pitch weather about four hours before first pitch. A board built in the morning for a night game is working from a forecast or a placeholder. On our own boards, 96% of the games on the mid-morning build had no published weather yet, which is why we rebuild through the afternoon and why each game is settled against the last board published before it starts.
The practical point for anyone betting a weather angle: the edge — where there is one — appears late, and the line moves when the forecast firms up. Checking a morning forecast is fine for deciding what to watch; the decision belongs to the last few hours.
6. What to Do With It
- Weather is a suppressor first. Cold and wind blowing in take home runs away more reliably than heat and wind blowing out add them.
- Compare with the park, not the league. A hot game at a hitter's park in July is not news; a cold, wind-in night at the same park is.
- Respect the parks where it is real — Wrigley with the wind, Coors with the altitude.
- Weather adjusts the hitter; it doesn't replace him. The batter's own power moves home run odds far more than any condition — the batter beats the pitcher and the streak.
7. Frequently Asked Questions
Does temperature affect home runs?
Yes. In four MLB seasons, starters homered in 8.9% of games played under 55°F and 13.3% of games at 85°F or hotter. Much of that gap is April versus July and which parks are cold, but even against the same ballpark in the same month, cold games ran about 1.7 points low.
Does wind blowing out increase home runs?
Less than the reputation. League-wide, games with wind blowing out at 10 mph or more produced home runs in 12.0% of starts, about half a point above what those ballparks normally give up. Wrigley Field is the exception: wind out there produced 16.7% against 8.3% with wind blowing in.
Does wind blowing in reduce home runs?
Clearly. With wind blowing in at 10 mph or more, starters homered in 10.3% of games against 11.9% for the same ballparks overall — a drop of about 13%. In our data, weather does more to suppress home runs than to create them.
When is MLB weather known for a game?
MLB publishes a game’s first-pitch weather roughly four hours before the game. Anything built earlier in the day, including morning projections and email picks, is working from a forecast or a placeholder. Check the latest update close to first pitch before acting on a weather angle.
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