There have been historically low HR rates this season. Although weather hasn't helped, it appears MLB has made another big change in further deadening the baseball.

Read on if interested: Ballpark Pal uses a model for park factors that estimates the "expected" outcome of a fly ball based on:

Weather (temp, wind, humidity, etc.)
Launch angle & speed
Spray angle (direction of the fly ball)
Stadium

It produces something like this:
HR: 48%
XBH: 22%
1B: 18%
Out: 12%