My hat is off to all of you who run in heat and humidity, and in the city! I don't know how you do it.
My family took a brief trip to Washington, DC over the long weekend, and I ran twice. Both times, it was at least 80 degrees and 90%+ humidity by 8am. It was brutal for this fair-weather newbie, who is used to running in temps between 50 and 65 degrees, even on a sunny mid-day. (Our average high temp in July is 68 degrees. Not average temp--average HIGH.) I ended up quitting early and walking part of the route, drenched in sweat. Of course, I then spent the entire day on my feet standing and walking around all the museums.
If it hadn't been for the heat, though, it would have been awesome. I walked from our hotel, then ran along the Ellipse, along the ponds past the Vietnam memorial, up and down the steps of the Lincoln memorial, past construction on the reflecting pool (no pool there currently) past the Washington monument to the rest of the mall and back along the Ellipse. One day, I will run that loop, adding the Jefferson Memorial, during cherry blossom time. I think that would be incredibly beautiful!