I lived in the Harrisburg area for almost 8 years (and grew up in the Lehigh Valley), have a degree in geography, and work in transportation, so I think my 2 cents have value (then again, maybe not

).
In general, in terms of "Baltimore/Washington influence" in south central PA, it really depends on where you are located in south central PA.
*The York and Hanover areas and in general most of York County (excluding the northern third closest to Harrisburg) definitely falls more within the Baltimore sphere than anything else. Those areas, especially Hanover, do get Baltimore TV stations on cable. Sports-wise, in baseball the Orioles are definitely the most popular team, though the Phillies have a sizable minority of fans. Those are the 2 "local" teams there; there are only a small number of Pirates fans there. In football, it is a more even split between the Eagles, Ravens, and Steelers (with a few Redskins fans thrown in), though I suspect when the Colts played in Baltimore there were a higher percentage of Colts fans then than Ravens fans today in York County.
*The Harrisburg area has distinctly less of a Baltimore or Washington influence than the areas immediately to the south do, but it is definitely still there. Sports-wise, the Phillies, 76ers, and Flyers are clearly the most popular teams in their respective sports in the Harrisburg area. Regarding the other MLB teams, the Orioles would almost definitely rank ahead of the Pirates (and definitely ahead of the Nationals) but well behind the Phillies. There are a decent number of Yankees (and to a lesser degree, Mets) fans in the area (and all of south central PA) due to a decent number of NYC area transplants and in the case of the Yankees, bandwagon fans. In football, the Eagles and Steelers are pretty close in popularity (with the Eagles probably being a shade more popular) and are the most popular teams. There are a few Ravens and Redskins fans in the Harrisburg area, but a lot fewer than either Eagles or Steelers fans. The Harrisburg Patriot-News gives more than standard coverage to all 4 teams, though in many cases the articles are AP articles. Like with the Yankees and Mets, there are a few Giants fans running around too (in addition to the present-everywhere handful of Cowboys fans).
*The Lancaster area is sort of the inverse of York in terms of baseball fan affiliation, with the Phillies being clearly the most popular team and the Orioles having a decent-sized minority following. Like most of south central PA, there are few Pirates fans. In football, the fan affiliation is like Harrisburg, except that there are a higher percentage of Eagles fans, a lower percentage of Steelers fans, and a higher percentage of Ravens fans (though still not as many Ravens fans as Steelers fans). The number of Redskins fans is lower too.
*The Lebanon area is similar to the Harrisburg area except that the Baltimore influence (and fan affiliation) is less there than in Harrisburg. In other words, there are few Orioles fans there and very few Ravens fans there. There are also few Redskins fans there.
*The Gettysburg area tends to be more strongly aligned with Washington relatively-speaking than all other areas in south central PA, mainly because it is closer and more directly connected to DC. Having said that, in baseball the Phillies and Orioles are the popular teams (I'm guessing relatively close to an even split, probably a few more Orioles fans than Phillies fans), while the Nationals are still not that popular. In football, again there is a mix between the Eagles, Steelers, Ravens, and Redskins (probably a more even mix between the 4 teams than anywhere else in PA).
*The Chambersburg area, compared to the Gettysburg area, tends to have a stronger Pittsburgh influence and a weaker Philadelphia influence. The Orioles are probably the most popular baseball team, with the Pirates second, and the Nationals and Phillies behind both teams. In football, the Steelers are probably first, with the Redskins, Ravens, and Eagles behind them in that order.
Though the thread is about south central PA and not eastern PA, I have to comment A) Mets fans do not take over Citizens Bank Park when the Mets play there (maybe 20-25% of the fans at most) and B) northeastern PA, as previously noted, has always been a strong New York fan area (even before the NYC area transplants moved to the Poconos), though Philadelphia affiliation is a little stronger. The reason for the many Mets fans is that getting to CBP is easier for many Mets fans in central and even northern NJ than getting to the Shea Stadium area. As for the fan breakdown in northeastern PA, in football the 3 primary teams are Eagles, Steelers, and Giants in that order while in baseball it is close between the Phillies and Yankees.
Finally, here's a rundown of fan affiliation of some people I know from the areas in question:
*A friend of mine who grew up in Hanover is an Orioles and Ravens fan (and was a Colts fan when he was young).
*Another friend of mine who grew about 10 miles north of Hanover is an Orioles and Colts fan (he didn't convert when the Colts moved). He also likes the Wizards and Georgetown in pro/college basketball.
*My father and his family were from northeastern PA (down river from Wilkes-Barre in Bloomsburg). My father grew up in the 1950's as a Yankees and (football) Giants fan, though the Phillies were his National League team. His best friend growing up was a Phillies and Eagles fan.
*I grew up about 10 miles north of Bethlehem as a Philly sports fan, following the Eagles, Phillies, 76ers, and the Big Five college basketball teams most closely. (I also follow Lehigh and Lafayette in college sports.) The Steelers and Giants (or vice-versa) in football and the Yankees in baseball are the primary secondary teams in the area where I grew up (Lehigh Valley).