Really, San Diego to the coast
I was born in Lynwood, CA and lived there until 1999 when we moved to SW Missouri. I just turned 69 years old and wish I had the opportunity to cruise HWY 1 and 101 all the way from National City to Crescent city as I'd done many times before, where I went from 100 degrees to 40 on the coast right below Brookings, Oregon, all in the same couple of days!
There is a MAJOR difference in areas of low to no Humidity versus areas where it is ever present!
We are in a heat wave thing here now in SW Missouri as is the entire heartland and this makes riding for pleasure a chore instead of fun. The temperature will get to you much more in humidity as I'm sure our fellow riders that put up with it can tell you.
I went for a 111.2 mile ride yesterday morning, in SE Kansas, in 95 degree heat, with high humidity and extremely BRIGHT sunlight and it got to me a little, until a big plate of Eggs, Sausage, Hash browns, Wheat Toast and prodigious amounts of iced tea brought me back to life and then the 40 additional miles back home didn't seem too bad.