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.

       The heat index will soar to a life-threatening 103 degrees in Charlotte, North Carolina; 106 degrees in Nashville, Tennessee, and Shreveport, Louisiana; 107 in Memphis; and 108 in Little Rock, Arkansas, and Jackson, Mississippi.

       The heat will dissipate after Thursday, but it’s expected to return next week, with nearly two-thirds of the eastern U.S. facing warmer than normal temperatures.

       Click here for what you need to know to stay safe in the heat.