Shad are unable to viable spawn/fertalize eggs if water is below 55ish - you'd have to check my shad podcasts from years ago for the exact temps.
We're still at Peter Pan on the Disney scale of fish catching vs time
My standard timing is last two weeks of April into early May. Last year the best day was May 4. I had not seen fishing like that since April 12, 2011. If we had poppers we would have caught shad on poppers.
Search past shad episodes easily below: