Clouds gather over Fenway Park (Andrew Teman/ RedSoxSource and Flickr )

In an analysis of more than 35,000 Major League Baseball games, eleven performance measures from batting, pitching, and fielding were related statistically to varying levels of cloud cover. More specifically, the study evaluated whether the collective differences in offensive production, pitching, and fielding led to changes in “home field advantage”.

Among the principal statistically significant results are:

* Cloudy skies benefit the batter while clear skies benefit the pitcher

* Offensive production generally declines during clearer-sky games compared to cloudy-sky games.

* Batting averages increase under cloudy conditions

* Pitching performance increases when skies are clear with strikeouts having the strongest response

* The number of errors increases during clear-sky games (it’s also noted that errors increase during all daytime games when compared to games played at night)

* Fly outs and ground outs increase between clear- and cloudy-sky games

In all parameters of baseball performance the differences between clear and cloudy conditions are quite small. But in a game where small differences in statistics over a season or career (such as batting average or ERA) can be key to team and individual player success, the effect of clouds cannot be totally dismissed.

Bottom line: Although the impacts due to cloud cover influence both away and home teams in much the same way, overall the study found that the home team winning percentage increases during clear-sky conditions when compared to cloudy conditions. Across all games the home team wins about 54% of the time, but the home team advantage is more pronounced (56%) when skies are clear.

Post script:

As an avid, fervent, dedicated, enthusiastic, zealous, etc. fan of the Boston Red Sox, I’m often asked as a bonafide meteorologist what weather should be wished for that might increase the odds of a Red Sox win (especially when playing the N.Y. Yankees). My usual response is a simplified rundown of results from several studies (see links below) that have assessed how various weather elements can impact Major League Baseball games. More often than not I have to remind inquirers looking for any possible advantage that, whatever the weather (for better or worse), it affects both sides the same.

Does this study change that view? While seemingly a small factor, sky conditions could be important in a close race between, for example, the Red Sox and Yankees for the American League pennant. But it’s really more complicated than that.

There are a number of factors which compromise the interpretation of the results, which the authors of the study readily acknowledge.

Nominally, one might expect that bright sunshine would be visually disadvantageous. The advantage to the home team may simply reflect its ability to compensate because of its familiarity with the ballpark in regard to, for example, characteristic locations of shadows and stadium architecture. Items not taken into account include the height and cloud type where, for example, high thin cirrus cloud cover would create brighter conditions than low stratus with less light induced glare.

Also, average cloud conditions over the course of a game uniquely define the game as falling into the category of cloud or clear. No account is taken of changing conditions, for example, of clouds moving in to cover the sky during the course of a game. Moreover, changes in the amount of cloud cover can alter other meteorological variables, such as temperature and humidity, which cold impact player performance.

Baseball weather links :

Aerodynamics of Baseball : NASA interactive simulations; specify weather conditions and see effects on hitting and pitching (great fun)

Weather and baseball (from Capital Weather Gang)

Can the wind make Strasburg’s fastball faster? (from the Capital Weather Gang)

How does weather affect baseball?

SportsPlayersNetwork: How the weather affects baseball