Personally, I have found that the further south you go, the less you see helmets, especially in areas with a large "retirement" population.
I rode 21.5 miles this morning. It is just slightly less humid and hot than yesterday, probably about 80-83 while I rode. I was delayed a bit by having to deal with one of my young adult clients who has fallen apart. Oy, always on my day off.
I rode 5 miles, up a street that's a series of hills, which are not steep, but keep coming, with some nice breaks, across the highway, and down a hill to the bike trail. It is really shady and was a good choice for today. It was quiet, too. Probably rode about 9 miles on the trail; I didn't go as far as I usually do, as I didn't want to do an out and back, as I am a little sick of riding home on the road I climbed to get to the trail. I stopped at the point where the new part of the trail ends and turned onto a lovely super shady road in the town of Carlisle. From there, I accessed the main road into Concord Center, which is pretty flat. Made it through the center, despite some ugly road construction and then scooted around West Concord center, by doing the reroute I do when I commute. The last 4 miles were not so shady, but it didn't feel half as bad as Monday's ride.
Tomorrow is the peak of our heatwave, with a real feel of 105 predicted. Although I may ride early AM (like 5), I will be safely inside my office. After that, looks like beautiful, typical New England, crisp, cooler (50's-70's) for a long stretch. And, my horrible allergy thing is finally gone, after 2 weeks.