Could the weather in Seattle REALLY be responsible for the Mariners' woes at home?
I don't believe the science supports this belief, which we've heard expressed frequently.
The idea is that cool, moist air...which we've seen a great deal in the parting days of our La Nina winter, spring and now "almost" neutral summer, is more dense, robbing hitters of distance.
Let's examine the elements of this belief: Air density does increase with cooler/decreasing temperatures -- that is, all other factors remaining equal, cool air is more dense than warmer air, which could conceivably increase the drag on a "hit" baseball, reducing the potential for "the long ball." The problem is, the impact would be small...and in fact, moist air is less dense, not more dense, than drier air. That would serve to counteract any increase in density from cooler air temperatures.
Don't believe this? Pull out your handy copy of the Periodic table of Elements. The air we breathe is mainly nitrogen and oxygen; water vapor is hydrogen and oxygen. Increasing humidity means proportionally greater amounts of hydrogen than nitrogen in the air. Hydrogen (#1 on the table) is a lighter element than nitrogen (#7 on the table), which is why water vapor makes air less dense -- and therefore, would tend to reduce the potential impact on a soaring long ball.
There's a more immediate fact to disprove this claim. Such conditions should impact both the home and visiting teams at Safeco; the visiting teams have done just fine. The Mariners' hitters scored 23 runs over 9 home games in June. Their opponents scored 37 runs. In July, our guys scored 22 runs over 7 home games (through Sunday, July 15), while their opponents scored 20. When the M's won in July, they tended to win big with scores of 6 or 7 runs. Those wins, by the way, didn't come on days that had markedly warmer or drier weather compared to days on which there were losses. That doesn't tend to speak of too much air resistence.
Our 'M's' will come around...