CHICAGO -- A dangerous heat wave will have more than half of the country sweltering over the Fourth of July holiday. Temperatures near -- and above -- 100 degrees Fahrenheit are combining with thick humidity to present serious health hazards.

The National Weather Service posted a reminder Friday that heat kills more people each year than tornadoes, lightning and floods.

Yeah, it's summer, and summer is hot; but heat can be dangerous. HEAT KILLS more people each year than any other weather hazard, including tornadoes,lightning, & floods. You take precautions for those. Give heat the same consideration during this #heatWavehttps://t.co/asAP108BNk pic.twitter.com/2XlPgc2w3Y — NWS (@NWS) June 29, 2018

In Chicago, the great outdoors is not so great -- heat so oppressive officials are warning the public to beware.

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"Safety is everyone's responsibility, so we remind everyone to stay hydrated and check on our neighbors and family," said Rich Guidice of the Office of Emergency Management and Communications.

The thermometer readings are in the 90s across the Midwest, but as any dog knows, when you add in the humidity it actually feels like 105 or even 110 degrees. Overnight, lows in the 80s won't cool down anything.

Eighteen states from New Mexico to Michigan have issued heat advisories, warnings or watches, making up a heat dome that is descending on 60 million people. A storm knocked out power to 30,000 of them in St. Louis, who now lack air conditioning.

The heat index is in triple digits in Kansas City, Des Moines and even Minnesota -- where the Minneapolis Star Tribune said the state is now like "Saudi Arabia with lakes." Denver's temperature on Thursday was a record-tying 105.

As the scorcher expands east, New York will bake this weekend and so will Vermont up to the border with Canada.

There are at least 80 outdoor activities scheduled in Chicago this weekend, from fireworks, rallies and concerts, meaning thousands are just gonna try to sweat it out.