I've been a few times in February. Usually, the low is 55, and the high is 75.
It's one of the best times to visit, because the crowds are very light, yet all the rides work. Rip Saw Falls will be down for maintenance, but JPRA and Popeye should be running.
I usually wear jeans with 2 t-shirts in the morning. If it's 50 degrees, then that's a little bit too cold, and I wear a jacket. In the afternoon, it warms up, and I've even gone on Popeye with my t-shirt off.
What you can do is dress warm for the morning, then change in the afternoon. You can go back to your car, hotel, or even get a locker at the front of the park.
In February, the parks close early, like at 6pm. So you'll be leaving as it starts to get cold again. Go to dinner, get to bed early, and get an early start the next day.