Living in the upper Midwest, I never say never since summer usually lasts a couple months and many years of late they are cool and cloudy. This year has been hot, sunny and glorious. Have been out in 90-95* with two polar bottles frozen prior to departure. I try to run a route close to lake Michigan which typically is 8-10* cooler than inland. I must say that I came close to an overdo in July on a 40 miler mid-day despite religious hydrating before and a few cliff bars and the aforementioned polar 20 ozers mid ride. Needless to say, that I am the exception to the rule here since most folks stop venturing outside by August in a hot summer. The majority population in Wisconsin consider 60* ideal and are looking forward to fall by Labor Day. Probably should mention that I was a serious runner before turning to the road and mountain bikes and loved a sweaty 5 miler in FL spring heat.