I was just up there the weekend on 6/25. About 18 miles south of Wellsboro, PA. It was mid 70's to low 80's during the day. It got kind of chilly at night. If I wasn't by the fire I needed more than just a t-shirt.
Looked like it was going to rain more than it did. Just a few quick passing showers. But they were welcome as they brought a nice breeze.
Check to weather for Wellsboro, it's very close to the trail. 2 great outfitters in Wellsboro. One is more geared for bikes, the other is a great all around outdoor store. Lots of maps of the trail and area, most are free even, on your right as soon as you walk in. Plus there's the Wellsboro diner, great place for breakfast.