Millions of people will have to brace themselves for an exceptionally hot July 4th week as a large swath of the eastern U.S. prepares for a heatwave — all as deadly wildfires continue to burn in the west.

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Almost 140 million people are under heat alerts from the Midwest to Florida and across the Northeast and New England. The heat is expected to ramp up through the week, with temperatures soaring into the upper 90s and 100s. Heat index values — or what the heat actually feels like to the human body — could reach 105 to 115 degrees.

Cities in the risk zone include Boston, New York City, Philadelphia, Baltimore, Washington, D.C., and Chicago.

On Tuesday, major to extreme heat risk is expected, with warm overnight temperatures offering little relief and increasing the risk of heat-related illness.

The heat will peak Thursday through Saturday for the Midwest, Great Lakes, Mid-Atlantic and Northeast. By July 4th, close to 100 new daily record highs will be set.

New York City is expected to receive temperatures as high as 95 degrees on Friday, with a heat index of 106. Washington D.C. and Raleigh will have highs of 103 degrees later on this week with heat indexes of 108 and 107 respectively.

Western wildfires

Over the weekend, numerous new wildfires erupted across the interior West, especially across Utah and Colorado.

Three firefighters were killed while tackling fires on the Colorado-Utah border this weekend. The victims were identified as 26-year-old Sydney Watson, 27-year-old Nick Hutcherson and 38-year-old Emily Barker, according to the U.S. Department of Agriculture Forest Service.

“We mourn the loss of three firefighters who answered the call to protect others and made the ultimate sacrifice in service to their fellow citizens,” said U.S. Wildland Fire Service Chief Brian Fennessy. “Our thoughts are with their families, loved ones, friends and crewmates as they face an unimaginable loss,” U.S. Wildland Fire Service Chief Brian Fennessy said in a statement. “These firefighters embodied the courage, professionalism and selflessness that define the wildland fire service.”

Two more firefighters were injured in the same incident and are receiving medical care, according to the forest service.

The largest of the fires, the Cottonwood Fire in southwest Utah, is now more than 93,000 acres and remains 0% contained, according to WatchDuty.com, which has been tracking the blaze.

On Monday, fire alerts remain in effect for the Four Corner states — Arizona, Colorado, New Mexico and Utah — as well as parts of Wyoming, South Dakota and Nebraska.

There is an elevated risk for wildfires across the Four Corner states and Southwest, with the risk on Tuesday increasing to critical once again for parts of Utah, Colorado, Arizona and New Mexico.