Average Date of Last Freeze in the Spring across Central Pennsylvania:
These graphics show the last freeze in the spring (above) and the first freeze in the Autumn.
You can see that the growing season in McKean County lasts from May 20th through September 20th, while the growing season in Lancaster County runs from April 15th through October 20th. Therefore, crops can generally grow for two months longer in Lancaster, PA versus in Bradford, PA.
Between these dates (in the warm-season), your National Weather Service Office in State College, PA will issue Frost Advisories (minimum temperatures between 33 and 36 degrees) and Freeze Warnings (minimum temperatures of 32 degrees or colder), as necessary.
Average Date of First Freeze in the Autumn across Central Pennsylvania: