As a baseball flies through the air, the air pushes back against it, resisting its motion and decreasing the distance the ball travels. If you don't believe air can provide much resistance, stick your arm out of a car window at 60 mph and feel the push. The density of air is different from place-to-place and from day-to-day depending on temperature, humidity and air pressure.. In thin (or low density) air a ball can travel faster and farther because there's less air resistance. Let's breakdown the baseball importance of these atmospheric variables:

1. Pressure. Air under low pressure is less dense, or thinner, than air under high pressure. This is the main reason long balls carry farther in Denver-the atmospheric pressure at that altitude is always about 15% less than sea level pressures. A hit that would have flown 400 ft at sea level would carry to 430 ft in the thin air of Coors Stadium. This permanent effect of Denver's high altitude is duly noted by the oddsmakers, however, resulting in totals typically in the 12-14 range, reducing the opportunity to simply bet OVERS and win most of the time. The day to day pressure changes of the atmosphere, however, are not considered by the oddsmakers, but these daily pressure differences at stadiums caused by the meanderings of the high and low pressures depicted on weather charts are very small. On a low pressure day the pressure is only one or two per cent lower than on a normal day, so a 400 ft shot would only carry a whopping 402 ft! Obviously this effect is too small to worry about, especially since there are other atmospheric factors that actually make a big difference-read on!

2. Humidity. Air with high humidity is less dense, or thinner, than dry air. But this effect so slight it would only account for a long ball traveling a few inches farther on a humid day. There is, however, a significant and unexpected effect of humidity. According to Professor Robert Adair, the dean of baseball physicists, a baseball in a humid environment is actually heavier and less elastic than a dry ball, and, therefore, cannot be hit as far. The exact amount of this effect can only be determined experimentally, but, based on the data we've seen, we estimate a 400 ft shot on a day with average humidity would carry 415 ft on a very dry day with low humidity.

3. Temperature. Warm air is less dense, or thinner, than cold air. A would-be 400ft shot at 75 degrees would carry 408ft at 95 degrees.

4. Wind. Air moving along in the same direction the ball is flying pushes back less on the ball, allowing it to travel farther. In fact, the wind is very often the single most important thing to consider about the weather when betting baseball totals. A 400ft shot in calm conditions would turn into a 445ft blast with a 15 mph wind directed out to center field. So you can see on many occasions wind is more important even than the altitude in determining the total runs scored in baseball games.

Source: www.Sportsweatherpage.com