I got that, too. I have a trip scheduled for October to MSP, but I do not really see an advantage to paying full price now just to get half off then. Especially since I have no plans to go now.
This seems to be a safe promotion, full price during biting fly and mosquito season for half price during rainy season.
(Apologies to MN, I could not help myself. It is really bad here. Hot and humid. I hear it will change later in the week. Hotter and humider. And, it's worse in August.)