The MLBGameSim.com project has been completely different than our other sims.

One thing that has been abundantly clear is there are factors in baseball that are outside of just the matchups of pitcher versus batter.  The main factor that can be a factor is the weather.  There are two driving factors when it comes to the weather, temperature and wind direction. 

In fact in our research, when the wind blows out at 20 mph or more HR rates sky-rocket.  Temperature is equally important, as batting averages can jump as much 13 points for a game played at 70 degrees versus a game at 95 degrees.

Temperature G BA SLG ISO HR/AB
Less than 40 310 .251 .383 .132 .023
40-49 2186 .255 .389 .134 .024
50-59 7530 .255 .395 .140 .026
60-69 20808 .257 .401 .143 .028
70-79 30500 .264 .415 .151 .030
80-89 22944 .269 .428 .159 .032
90+ 6110 .277 .445 .169 .034

Source

Naturally, we had to consider this research in our simulations on MLBGameSim.com.  Anytime you are simulating from the predictions page, the weather will automatically be factored in.