US heat wave stretches into Midwest, heading for Northeast: Latest forecast

A relentless heat wave that has had a swath of the southwestern United States in its chokehold is stretching into the Midwest on its way to the Northeast this week.

The National Weather Service has issued heat alerts that are in effect on Tuesday for 45 million Americans across a dozen states, from Southern California to Montana, through the Great Plains and back down to South Florida.

The weather forecast for Tuesday shows temperatures will reach or exceed 110 degrees in cities like Palm Springs, California; Phoenix, Arizona; and Las Vegas, Nevada. Temperatures in the 100s are expected from Texas to Nebraska.

Heat index values -- a measure of how hot it really feels when relative humidity is combined with the air temperature -- are forecast to be in the 100s for even more places, including Kansas City, Missouri. It's the hottest time of the year for this area and these high temperatures aren't too out of the ordinary there.

Arizona's capital is on a record stretch of 25 consecutive days with temperatures at or above 110 degrees. Overnight temperatures in Phoenix have also not dropped below 90 degrees for at least 15 days.