DD I don't think I have ever heard you so professorial. Good points though. \:D

Lots of factors in addition to temps. -- photo period , water quality (chemical and visibility [ muddy water]) , fish condition , forage base condition (spawn suppression) etc. Think about this , these are just a bunch of factors that effect the timing of an event. If they were all the same ( as in all other things being equal) would you have one spawn day/week (all at the same time)? That may be part of the reason it is spread out in lakes where the water temps. allow a longer possible period. In that situation the other factors become more of an effect because the constraints of minimum water temps. are removed. Thus more options which are effected by other factors (than temp.) and thus more potential for extended spawn time and variation based on the other factors in southern lakes.