How Do Ballparks and Weather Affect MLB Betting Totals?

Ballparks and weather change how far a batted ball travels, and a baseball total is mostly a forecast of how many balls will travel far enough. The effects are real and they're large. By Baseball Savant's Statcast park factors for 2024 to 2026, Coors Field produced 25% more runs than average for the same hitters and pitchers, while T-Mobile Park in Seattle produced 15% fewer. Heat adds home runs at a measured rate of about 2% per degree Celsius.

The catch for bettors is that none of this is secret. Sportsbooks post totals with the park and the forecast already in them. The edge, when there is one, is in knowing which of the numbers you read about is actually priced and which is not, and in the forecast changing after the line goes up.

What a park factor measures

Baseball Savant sets every park factor so that 100 is average. A park at 125 for runs is one where hitters and pitchers who played there and elsewhere saw 25% more runs there than their performance in other parks predicted. The comparison is built player by player, controlled for handedness, which strips out the fact that some teams simply have better hitters.

Three-year rolling windows are the sensible default, because single seasons are noisy. The 2024 to 2026 window, read in late September 2026:

Park	Runs	Home runs	Strikeouts
Coors Field (Rockies)	125	108	90
Fenway Park (Red Sox)	106	87	97
Chase Field (D-backs)	106	93	90
Dodger Stadium (Dodgers)	102	123	102
Yankee Stadium (Yankees)	102	118	104
Wrigley Field (Cubs)	96	106	101
Oracle Park (Giants)	94	79	96
Globe Life Field (Rangers)	88	93	101
T-Mobile Park (Mariners)	85	98	116

The columns disagree with each other, and that is the useful part. Fenway is a run-scoring park that suppresses home runs; its doubles index in the same window is 120, so balls that would leave other parks stay in and still do damage. Dodger Stadium plays roughly neutral for runs but at 123 for home runs. A total and a home run prop in the same park can call for opposite leans. Seattle's 116 for strikeouts is the number to carry into a pitcher strikeout prop there.

Why Coors is different: altitude

Denver sits at about 5,280 feet. Alan Nathan, professor emeritus of physics at the University of Illinois and a long-time researcher on the flight of the baseball, puts the air density there at about 82% of sea level. Thinner air means less drag, so a fly ball carries farther. His estimate: about 5% farther at Coors than at Fenway, all else equal, which turns a 380-foot drive at Fenway into one of nearly 400 feet in Denver.

Thin air also hurts pitchers in a second way. Movement on a breaking ball comes from the same air that slows a fly ball, so an identical pitch breaks only about 82% as much at Coors. Hitters get a straighter ball to hit.

The Rockies store their game balls in a humidor, and Nathan's model predicted it would cut home runs at Coors by 27.5% against an observed drop of about 25%. That helps explain why Coors's home run factor (108) is far less extreme than its run factor (125). The ball stays in the park more often, but it still falls in: Coors's hits index is 117 and its triples index is 214, the highest in the league.

Temperature: roughly 2% more home runs per degree

The cleanest measurement comes from a 2023 study in the Bulletin of the American Meteorological Society by Christopher Callahan and colleagues at Dartmouth, built on more than 100,000 MLB games and Statcast batted-ball data. A 1°C rise in the day's high temperature raised home runs in open-air games by 1.96% (95% confidence interval 1.5% to 2.4%). The effect was larger for day games (2.4%) than night games (1.7%), and small and statistically insignificant under closed domes.

Worked through for a typical game: the study's average is 2.38 home runs a game. A day 10°C (18°F) warmer than normal for that park multiplies that by 1.0196 raised to the 10th power, about 1.21, which gives about 2.89 home runs. That's half a home run a game. Each home run is often more than one run, so it is not trivial for a total set at 8.5.

The mechanism is the same as altitude: warm air is less dense. The study confirmed it by holding launch speed and angle fixed and still finding more home runs on hot days.

Parks don't respond equally. Dartmouth's release on the study, looking at each 1°C of global average warming rather than a single hot day, estimated more than 15 extra home runs a season at Wrigley Field, an open-air park with relatively few night games, and one or fewer at domed Tropicana Field. Retractable roofs complicate every one of these estimates, because the roof decision is made on game day.

Wind, and why Wrigley gets the attention

Temperature is one number for the whole park. Wind has a direction, and Wrigley Field is the park best known for it. What stands out there is less how hard the wind blows on average than how much it changes from one day to the next.

David Kagan, writing in The Hardball Times in 2015, measured Wrigley's wind in 2014 at an average of 8 mph with a range from 1 to 23. He also cited a 2007 Hardball Times finding that more than 23% of Wrigley fly balls became home runs with the wind blowing strongly out, against 13% with it blowing in. That is close to double. His physics estimate for the new left-field video board, treating it as a complete windbreak, was that it changes a fly ball's distance by only about 10 feet, damping the wind whether it blows in or out, and he said he could not give a definitive answer.

Read wind reports at the level of detail they deserve. "Blowing out at 12 mph" at one hour can be crosswind at first pitch, and a flag on the scoreboard is not the air at the height a fly ball travels.

Is weather already in the price?

Mostly, yes. A total is posted with the forecast in it, and books update it as forecasts and lineups change. A hot, windy day at Wrigley that shows up in the morning forecast will usually show up in the total before most bettors get to it.

What moves the price is the forecast changing. A total posted with a cool, calm forecast and then reset by a warmer, windier one moves in steps. Suppose an over 8.5 moves from -110 to -130. That's an implied probability of 52.4% becoming 56.5% (130 ÷ 230), about four points. If the weather news reached you before it reached the market, you had the -110. If you are reading about it after the line moved, the number you'd be betting has already absorbed it.

Two practical cautions. First, park factors are averages of seasons that already happened. A new wall, a changed fence height or a new ball can make them stale, and the three-year window lags behind any such change. Second, weather effects are averages too. The 1.96% per degree is the mean across every open-air game in the sample; any single afternoon has enormous variance around it, which is why a correct read of the weather can still lose. The Academy's guide to closing line value explains how to tell whether you were early to a move or just lucky.

For how a starting pitcher's line interacts with a park, see our guide to pitcher props. The series moves to hockey next, starting with the puck line and regulation bets.