Ornates can handle some cold. On the arid plains where they occur, the winters can be brutal. However, when you think about how things impact your turtles, you have to consider them individually. I couldn't just tell you, "Oh yeah, ornates hibernate fine". While that may be true in general, there are some things to consider. I keep ornates and deserts in the humid Southeast. Constant humid air is the enemy of wild caught ornates. I'm assuming that you have wild caught individuals. Luckily, most of PA is not as humid as the South. Humidity will be an issue for you, but not the only one.
Turtles use daylength and the sun's strength to predict hibernation. You may notice that your turtles enter and emerge from brumation regardless of temperatures (exceptions exist, of course). Where did your turtles come from? Most likely Texas, due to the casual laws there. That's where most of my stock came from. A turtle from Texas living in PA may be looking at the sun and thinking that he/she has two more months to go when the daytime temperatures are below freezing. Now, most turtles will begin to dig down anyway when it gets that cold, but I hope you're catching my drift. Basically, you've moved an animal that's lived its whole life in a small area. It has become accustomed to a certain climate and predictable seasonal changes. Now, you've thrown it a curve ball.
It's been a nightmare for me to acclimate my ornates and deserts to my backyard. I never should have gotten any wild caught adults, and I NEVER will again. Hatchlings and young juveniles are so easy to acclimate...they haven't developed adult habits yet. Be prepared, you may have to bring some ornates inside in November or February. The bad thing is, for an ornate, inside is sometimes even worse. I'm sorry to be so negative, but I'm bitter over the vet bills, antibiotic injections, tube feeding, floor space, and stomach ulcers that I've experienced from them. Luckily, once acclimated, I've never seen a hardier turtle. Plus, they have tons of personality once they get to know you.
Here are my adult male ornate and a young Desert Box turtle emerging from winter brumation.

