One thing to remember is that while heights are important, ridge placement is probably even more crucial, as is the depth of the layers. For example, the Euro has ~592dm over us by days 8-10, but 850s are 15-16, which often translates to 90 plus or minus a couple. The GFS is similar, brushing us with 20C 850s by day 11/12, but if we are worried about big heat, you'd be looking at 850s well into the 20s. This seems like run of the mill dog-days heat. Of course, it'll be humid as hell.