Home teams had a .266 batting average on cloudy days, the researchers found. That slipped to .259 on clear days. For the visitors, the batting average was .256 when it cloudy and .251 on clear days.
Obviously, if cloudy days are better for hitting, sunshine should benefit the pitcher, and that's just what they found.
Earned runs allowed by home pitchers were lowest on clear days at 3.93, climbing to 4.26 on cloudy days. For visiting pitchers the ERA was 4.50 in the clear and 4.68 under the clouds.
The analysis is based on statistics from 10,758 major league day games obtained from STATS LLC and weather data collected by the National Climatic Data Center, showing the conditions at the nearest National Weather Service office to each stadium at game time. The findings are published in the current issue of the journal Weather, Climate and Society.
Kent said he had expected to see better hitting in cloudy conditions but was surprised by how strong the effect was on strikeouts. Home pitchers averaged 6.65 strikeouts on clear days, but in cloudy conditions that fell to 6.22. For visiting pitchers, the drop from clear to cloudy was from 6.14 to 5.67.
"I was also surprised with the increase in home-team winning percentage from cloudy day games to clear day games. While I had anticipated that the home team would be better equipped to compensate for any potential disadvantages caused by increased sunlight, I did not foresee the increase in winning percentage that resulted," he said.
On clear days, home teams won 56 percent of their games and visitors 44 percent. When it was cloudy, that fell to 52 percent home wins and visitors 48 percent.
More at the link.