Used to look for Grannoms on the Little J and then Penns starting about the middle of April. Best J hatch I ever enjoyed was something like April 17th. Flies hatching from 8 AM and still going at 5:30 PM! Wish it happened like that more often.
I do remember one crazy early spring better than ten years ago when the Hendricksons were full on on Penns Creek in something like the second or third week of March. I recall a lot of seventy-degree days in March that year down in the Cumberland Valley.
Catskill rivers are high and getting higher. Saw a few chimarras and early stones yesterday, and I saw stones in early March, so no doubt you should have some fishing in Central PA now. A friend was headed down to Penns Creek this week. Don't know if he is back yet.