The current heat wave sweeping the country reminds me of the heat wave we encountered up Chicago way in 1995. Read more about it :
Basically, you have fatal humidity coupled with record heat and people living in a place where its too dangerous to open windows. A place where older people are more isolated, smack in the middle of a huge town whose officials didn't declare the warning until the last day.
We really shouldn't need a warning. If someone is feeling very hot, not drinking enough, or not sweating, things are getting serious. If you know someone who lives alone, living in a heat advisory location, call them up, check on them.
One of my best ways of cooling down when the power goes out is to get a basin of cold water and sit down with my feet in it. Get a cold glass of water, and sip it while relaxing in the shade. If you need some extra cooling, get a paper fan and use it. If you get your hair wet, the fanning feels even better.
If you're planning some hiking during hot weather, get an early morning start. Try to stop by a lake, creek or river at lunch time. Take a swim, get your clothes wet, and stay in the shade. Wait a while before continuing. Remember after 3 p.m things will start to cool down and you can get some more miles in.
One of the worse places to hike through during a heat wave on the Appalachian Trail is that cornfield north of Duncannon in Pennsylvania. I got through there when the leaves were only knee high, early June. Can't imagine what it would be like in July.
All modesty aside on the Pacific Crest trail, when we came near water, I would take off my shirt, rinse it in the stream and continue on. This is one time when a cotton t shirt is better than synthetic because it will absorb more water and dry much slower. Throw a cotton t shirt into your bounce box for the desert and Hat Creek Rim of the PCT if you can.
Three main words of advice if you're out on a trail : Drink, drink, drink.