I have a lot of relatives in Michigan and have never thought of it as a Hot place. Every time I have been there, it has been very temperate compared to where I left. Even on the 4h of July, we didn't want to be in the water or wet swimsuits for long. To my relatives, the high 70s were very hot because most people didn't have air conditioners or only had them in the bedrooms, and even a lot of public places didn't have AC or at least didn't turn it on except for a bit in August. I haven't been back in several years and have heard that it has been getting very hot for long periods of time. Everyone had to get AC.