Got an interesting text from someone today from someone who ran the marathon, finished in just about 3h (out of the fourth wave, so in the real peak of the heat of the day) and finished with a 107 degree body temperature and spent some time in the ice baths. He didn't go hypothermic but wanted to hear about my experience. And is a grad student at MIT, so we're going to hit up the Muddy when he is cleared.
But it's a) completely validating of my strategy of dousing myself in lots of water to stay cool and b) occurred even with temperatures in the 40s to maybe 50 (here's a weather station at BC, the temperature peaked around race start and was back in the
upper 40s by then time I went through). I thought a couple of times how silly it was to be drenching myself in water, since it was perceptibly cool while I was running, but kept at it, because I was feeling hot. I now know what it feels like. Still the fact that this guy had a serious EHS with temperatures in the 40s means that the dry air and high sun is a big deal.
It's also conditions which are somewhat specific to Boston. Where else do you run a marathon with the sun 60 degrees overhead with no tree shade and temperatures in the 40s? Most other spring marathons (high sun angle) start very early in the morning so you don't have to deal with solar noon, and are run late enough in the season (Burlington City, Grandma's, etc) that there is some shade. NYC starts at 10 a.m. too, but the sun angle is only 33 degrees and there is more shade at the end from buildings and trees. It's like running a race in cold, high desert, except at sea level. Some years, anyway.