Heat advisories are in effect from Texas to New Hampshire as dangerous temperatures grip the eastern half of the U.S.
In the Northeast on Thursday, the heat index — what temperature it feels like with humidity — is forecast to skyrocket to 105 degrees in Washington, D.C.; 103 degrees in Philadelphia; 97 in New York City; and 93 in Boston.
In the South, an extreme heat warning has been issued south of Memphis, Tennessee, and in eastern Arkansas and western Mississippi…