I've heavily contemplated doing northern Plains rather than like southern Plains for chasing. Everyone loves May and early June in OK/KS, however, I think farther north offers just as much in terms of severe and without chaster convergence. Only issue I think is you can pretty much book a two week period in OK during late May well out and the odds of having at least one event are high. Waiting until like deeper in summer when they are active up north is a bit of a challenge...especially when factoring in taking time off of work. Some jobs you need to gives like months in advance.