NEW YORK: Pools were packed and power grids strained as millions of Americans sweltered in stifling heat and humidity Thursday, with dangerous temperatures expected to hit major cities through the Fourth of July holiday weekend. The heat wave that has been broiling the Midwest began intensifying in the Northeast, with temperatures hitting or surpassing 100F (38C) in cities including New York and Washington. The heat index — which measures how hot it feels based on temperature and humidity combined — was even more merciless.

The National Weather Service has issued heat warnings and watches for much of the Midwest and East heading into the holiday weekend. In many places, the temperatures could shatter…

Sweltering conditions are expected to last through the weekend