MLB venue data
The Marine Layer and Baseball: What 2,232 West Coast Games Actually Show
By OverUnderWeather Research Desk
Every West Coast broadcast says it: the marine layer rolls in at night and the ball stops carrying. We tested it on 2,232 games at Oracle Park, T-Mobile Park, Petco Park, Dodger Stadium and Angel Stadium since 2021. The coastal parks really are low-scoring — but night games don't lose home runs, and the market already knows these parks play small.
The short answer
8.45 runs per game vs 9.06 at other outdoor parks — 0.61 fewer (t ≈ −6.1).
2.31 home runs per game at coastal parks, identical to everywhere else (2.31).
Night vs day: 8.45 vs 8.43 runs, 2.36 vs 2.23 HR. No significant drop — nights are only ~2°F cooler.
Coastal games finished +0.38 vs the closing total, in line with other parks. It's priced in.
What the marine layer is supposed to do
The Pacific off California and Washington is cold. On summer evenings, cool, moist air from over the water pushes inland under warmer air above, often bringing low cloud and fog. The baseball theory is simple: cool air is denser, dense air drags on the ball, and fly balls that would leave the park at 2pm die on the warning track at 9pm.
The physics is real but small. Air density depends mainly on temperature and elevation; humidity actually makes air very slightly lighter. So the test that matters is whether coastal night games are meaningfully colder — and whether scoring drops when they are.
Day vs night at each coastal park
| Park | Games (day / night) | Temp | Runs | Home runs | Night vs day |
|---|---|---|---|---|---|
| Oracle Park | 199 / 275 | 63.4° / 61.2° | 8.70 / 8.13 | 1.87 / 1.83 | -0.57 runs (t -1.41) |
| T-Mobile Park | 143 / 259 | 66.6° / 67.6° | 7.73 / 7.88 | 2.24 / 2.40 | +0.15 runs (t 0.40) |
| Petco Park | 158 / 314 | 71.8° / 68.2° | 8.17 / 7.98 | 2.25 / 2.15 | -0.19 runs (t -0.47) |
| Dodger Stadium | 100 / 304 | 79.2° / 70.4° | 8.79 / 9.06 | 2.59 / 2.90 | +0.27 runs (t 0.57) |
| Angel Stadium | 113 / 367 | 79° / 74° | 8.91 / 9.00 | 2.48 / 2.44 | +0.09 runs (t 0.19) |
No park shows a significant night-time drop in runs or home runs. Oracle Park comes closest: night games scored 0.57 fewer runs than day games, but at t = −1.41 that is directional only. Dodger Stadium — the park with the biggest day-night temperature swing (about 9°F) — actually produced more home runs at night (2.90 vs 2.59), the opposite of the lore. Every park here has at least 100 games in each group.
Where the effect does show up
Put the five parks together against every other outdoor park in MLB and the coast is clearly quieter: 8.45 runs per game versus 9.06 across 9,205 other-park games. But home runs are the same (2.31 vs 2.31). So whatever keeps West Coast scoring down, it isn't mainly fly balls dying in the night air — it's more likely park dimensions, pitching staffs, and cool air all day long, not just after sunset. Oracle Park, with deep right-center and 61–63°F game-time air, is the clearest example: about 1.85 home runs per game, the lowest in the group.
One caveat: the "other parks" group includes Coors Field, which pulls the league figure up. Results are raw averages and not adjusted for team strength or pitchers.
Does the market price it in?
Yes. Coastal games finished an average of +0.38 runs over the closing total (2,226 games with a line), versus +0.46 at other parks — totals at these parks are already set lower. Night games at the coast were +0.40 over the close, day games +0.34: no marine-layer edge at night.
The one result that cleared the significance bar is Oracle Park day games, which went +0.80 over the close (t = 2.55). We tested many splits on this page, so one significant result is roughly what chance alone can produce — treat it as something to watch, not a betting rule.
Related MLB weather guides
Method and sources
Open-air MLB games at Oracle Park, T-Mobile Park, Petco Park, Dodger Stadium and Angel Stadium from our MLB game conditions data, 2021–2026 (2,232 games; Dodger Stadium through 2025). Games with T-Mobile Park's roof closed are excluded. Game-time temperature is measured at each park's own coordinates. "Night" means first pitch at or after 5pm Pacific. Comparison group: 9,205 open-air games at all other parks. Closing totals from our closing-line table. Differences tested with Welch's t-test; results with |t| under 1.96 are reported as not significant. Raw averages, not adjusted for team strength; the 2026 season is partial. Data queried 12 October 2026. By the OverUnderWeather Research Desk.
Where this is applied
These findings feed the game-time read on every MLB venue page, using the same sample-size and significance rules published here.
OverUnderWeather Research Desk
Independent data analysis on public sports and weather records. Studies match historical game outcomes to archived game-window weather, apply pre-set sample and significance rules, and publish null results when that is what the data show. Editorial policy and corrections log.
Cite this research
Free to republish with a visible credit and a link to this page. Ready-made citations below — click to copy.
Frequently asked
What is the marine layer in baseball?
It is the cool, moist air that forms over the cold Pacific and pushes inland in the evening, often with low cloud or fog. Players and broadcasters at Oracle Park, Petco Park and Dodger Stadium have long said it 'knocks down' fly balls at night. Physically, cooler air is denser and slows the ball slightly; humid air is actually marginally less dense, so the effect is mostly about temperature.
Does the marine layer reduce home runs?
Not in a way our data can see. Across the five coastal parks, night games averaged 2.36 home runs versus 2.23 in day games (t = 1.76, not significant) — slightly more at night, not fewer. Coastal parks as a group average 2.31 home runs per game, the same as every other outdoor park (2.31).
Do West Coast ballparks score fewer runs?
Yes. The five coastal parks average 8.45 total runs per game versus 9.06 at other outdoor MLB parks — 0.61 fewer, a large, clearly significant gap (t ≈ −6.1 across 11,437 games). Note the comparison group includes Coors Field, and the gap is about runs, not home runs.
Which park is most affected?
Oracle Park is the coldest and lowest-home-run park in the group: 61.2°F at night and about 1.8 home runs per game. Its night games scored 0.57 fewer runs than its day games, but that difference is not statistically significant (t = −1.41), so it is directional only.
Does the betting market price in the marine layer?
Yes. Coastal games finished an average of +0.38 runs over the closing total, close to the +0.46 seen at other parks — so the market already lowers totals at these parks. One exception stands out: Oracle Park day games went +0.80 over the close (t = 2.55), but it is one result among many tested, so treat it with caution.
Why don't night games show the effect?
Mostly because the temperature barely changes. On average, coastal night games are only about 2°F cooler than day games (68.7°F vs 70.6°F); Dodger Stadium is the exception at about 9°F. Day games also tend to be getaway games with different lineups, which muddies any simple split.