Dont know if it applies to 40 degrees, but My hen has hatched chicks in the early spring when we've had miserable cool and rainy, yucky weather- you know, it was probably like that in PA too.
She not only hatched them, but had them out free ranging in the wet miserable stuff, then would bring them back into the pen and sit on them- on wet ground.
I did my best to keep dry straw under her, but she wanted nuthin to do with it. Amazingly, the babies all did fine. I on the other hand got more gray hair! I had a chicken wander off just before a blizzard in January. When she didnt make it back, I figured she was a gonner. Darn if she didn't wander back into the barn with a single little chick one day! There was still snow on the ground. So, never fear, all those downy feathers serve a purpose! My Lucy is still on 4 eggs and yes, its freezing here- they said frost tonight. No sign of pips here yet. Maybe mine are duds, or maybe they're waiting for tomorrow when it will back in the seventies. Good luck!
Well that is good to know, usually mine who are sitting are inside the barn. My new runs are apparently a little too big, as she was able to hide these eggs from me until she started sitting on them. Obviously mine are taking a bit longer than normal (yesterday was day 28), so I wouldn't give up yet, yours may be a day or 2 late as well. Good luck to you as well!