Weather is an aspect of the environment that affects all of our lives, whether it is checking the weather channel before deciding to go to the beach or how many layers of clothes one should put on. Weather also plays a factor in the outcome of MLB games and below are four main factors that should be accounted for.
The amount of air pressure that is present affects the distance of fly balls travelled. With low pressure, air becomes thinner and with high pressure, air becomes thicker. During days with low air pressure, fly balls tend to travel further whereas during days with high air pressure, fly balls are unable to gain as much momentum. Air pressure tends to play a role in the over/under total for MLB games since fly balls that would be outs under high air pressure may end up becoming home runs under low air pressure. In the U.S., some cities with the least variation in air pressure include Miami, San Diego, Los Angeles, Tampa Bay, and San Francisco. On the other hand, some U.S. cities with the most variation in air pressure include Boston, Denver, Detroit, New York City, and Minneapolis. One city in particular, Denver, Colorado, has extremely low air pressure, which results in fly balls being able to travel further. This is why the Colorado Rockies usually place in the top five in terms of runs scored due to the fact that fly balls are more prone to turn into home runs. However, Las Vegas oddsmakers take this into account, which is why games played at Coors Field (Colorado Rockies home stadium) tend to have higher than normal totals.
Wind Direction and Speed
Wind also plays a factor in MLB totals, which depends on the direction that the wind is blowing as well as the speed of the wind. If the wind is strong and blowing towards the outfield, there is a greater chance that fly balls will get carried by the wind, resulting in home runs. This essentially places a handicap on pitchers that rely on fly balls to induce outs (e.g. Marco Estrada, Chris Young) since their room for error shrinks. On the other hand, if the wind is strong and blowing towards the infield, there is a greater chance that well-hit balls on the verge of going over the fence will get swallowed up by the wind and brought back into play, resulting in fly ball outs. This is extremely beneficial for fly ball pitchers, and pitchers in general, as it provides an extra cushion in the event of a poorly located pitch. Strong winds blowing towards the outfield usually result in high scoring games whereas strong winds blowing towards the infield usually result in a pitcher’s duel, with lower scoring games.
When humidity is high, air becomes thinner than if there were no humidity (dry air). Although fly balls travel further in the midst of thinner air, the increase distance travelled is relatively insignificant. However, with high humidity, moisture gets absorbed by a baseball, essentially increasing the weight of the ball compared to a completely dry baseball. As a result, a heavier baseball becomes more difficult to hit out of the park.
Early in the season, temperatures tend to be much warmer compared to the end of the season, when temperatures begin to drop. Since a ball travels further in warm air than cold air, backing the over for totals when the weather is warmer (holding all other factors constant) makes for a smarter move while backing the under for totals when the weather is colder (holding all other factors constant) makes more sense. This is due to the fact that warm air is simply thinner than cold air, allowing fly balls to travel much easier.