Hersheypark has a weather monitoring station in park, thus the seemingly strick severe weather policy. With that said, the likelihood of a thunderstorm this October, well... lets just say snow seems to be more of a threat.
I have been to HPITD each season for the past five years. While Saturdays do tend to be a bit busier, its very unpredictable. Make sure to dress very warm as well, for we found that Storm Runner in the low 50's is bone chilling.