Well those extra storms probably just go somewhere else because of the change in wind pattern that the El Nino brings, eh? At any rate I'd just like to point out a potential clue to your springtime predictability barrier problem. You mentioned, if I understood correctly, that a La Nina pattern during winter months leads to an increase in the North American Monsoon in late summer. That's at least one part of a very big climate puzzle crossing that barrier that involves both the ocean and atmosphere. Not really sure if it's possible to even find that rabbit hole let alone getting to the end of it :) Good luck.