I will have to say the info I have posted is from a Missouri Fish biologist at Table rock, the article is for the Fall River/Toronto Fisheries District. The article does say these 2 areas are the same latitude which is also the same latitude as the southwest tip of Indiana. So I'm assuming the crappie spawn time would be for southwest Indiana(Evansville) and would be way off for my Midwest area and way way off for N. Indiana.
Monday I fished a small lake with a large 3fot cove and the temp was 62 late evening, it was 58 around noon. All I caught was small bass but one guy said he caught 2 male crappies. So I guess my area is close to temps for spawn.
My gold fish spawned early this year and they are the only fish that I'm certain of having keep them in ornamental ponds for over 30 years. :-)
I don't question the biologists know something about when the spawn happens and my experience is that it happens about the same time every year. I also plant my garden at the same time every year so I don't find it remarkable but I can plant my garden a few days earlier on average than when I lived in the suburbs in a valley that always had some late frosts.
The daylight hours mentioned are from mid April to mid May so that is going to catch most of the Crappie spawn for latitude 38 to 39. If you go fishing from mid April to mid May you will catch the spawn here. That is what I would call a pretty inaccurate forecast if you were say planning a vacation around the spawn making the utility of the information fairly useless for most people.