Pretty logical, actually --- the weather will be in the 50s, but a steady rain will start at about 6pm and last all night. Rainy weather usually helps the team that can run the ball more, while slowing down the more pass-happy team. Also, the bad weather helps the squad with better special teams.
Ohio State's two main weaknesses this season have been their pass defense (ranked 109th), and giving up the big play. Penn State's best strength on offense has been their pass game, while their run game has left much to be desired. This wet field may help slow down the PSU pass offense, and help OSU negate their achilles heel on defense.
OSU's strength has been their (10th-ranked) rush offense. With Braxton's recent injury, OSU will likely limit his carries, so I think Hyde gets 20-25 carries, and Rod Smith may take 6-8 carries. Yes, PSU's strength on defense is against the run (ranked 20th), but they haven't faced a foe with combination of athletic ability & muscle in the run game like Ohio State. Despite Miller's health, he will still pose a solid threat as the most athletic QB PSU has faced by far. They have to stay honest against the read-option & Miller will burn them a few times. Carlos Hyde will eventually wear down the PSU front 7, and OSU will pull away in the 4th quarter with consecutive pounding carries by Hyde.
Lastly, even before this game the special teams edge tilted to OSU...but again the weather can't help PSU's abysmal kicking game. Look for a long punt return by Philly Brown and/or Chris Fields, too. PSU does not carry the traditional depth on special teams that they've had the luxury of employing like in year's past.
Before I was a little on the fence and thought OSU would win a close one...now I say OSU by 10 or more. Ohio State: 31 Penn State: 16