Wrigley is a weird place for totals. Usually when you see a total at 7 it means the game is going under. When you see a total at 12 it usually means the game is going over. So that was the 1st thing I thought of.
Under is 6-1 in Cubs last 7 home games with the total set at 7.0-8.5.
With Harden on the mound, this may be asking for a lot, but I dont see him giving up more than 1 run. In fact he hasnt given up more than 1 run as a cub. He's only given up 3 runs in 4 starts as a cub and all 3 were solo homeruns. With the weather conditions on his side today, it's probably going to be tough to get it out of wrigley so I wouldnt be surprised if he held the astros scoreless today.
Wandy Rodriguez is the question mark. His problem has always been on the road, but he hasn't given up more than 4 earned runs in any of his 7 road starts.
So going by recent history, with these weather conditions, anything more than 5 runs between the two would be surprising to me. I'll just hope that the bullpens can hold their own today.
Adrian Johnson behind the plate doesnt hurt either. He's not a huge under ump, but not many runs are scored in his games and more of his games stay under than go over.