Dangerous and potentially record-setting heat wave to scorch millions this July Fourth

By Meteorologist Briana Waxman

(CNN) — Millions of Americans across the eastern half of the US are facing a prolonged stretch of dangerous and potentially record-breaking heat as Americans get set to head outdoors to celebrate the country’s 250th Independence Day.

The oppressive heat and humidity will hover over the Midwest early this week, then move into the Mid-Atlantic and Northeast by Wednesday. The sprawling heat dome will linger over the East, particularly the I-95 corridor, and peak by Friday, just in time for the long Fourth of July weekend.

Many areas will endure consecutive days of temperatures near or above 100 degrees Fahrenheit, while humidity will push the heat indices, or “feels like” temperatures, as high as 110 degrees or more.

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Heat waves worldwide are becoming more harsh and frequent because of human-caused warming from fossil fuel pollution. The record-shattering heat waves in Europe last week and in the western US in March are two recent examples.

Heat is also the deadliest type of weather in the US, with a higher annual average death toll than tornadoes, hurricanes and lightning combined, according to weather service statistics.

The heat won’t end at sunset

The biggest concern isn’t just how hot afternoons become, but also that the heat won’t stop when the sun goes down. The combination of several consecutive hot days and exceptionally warm nights across a huge geographic area poses a serious health threat.

Over 100 daily record highs could be tied or broken, but over 250 record warm overnight lows could be challenged this week alone.

The message from the National Weather Service has been consistent: this heat wave is different. In eastern Virginia, the weather service says this could be the region’s most significant heat wave since July 2012, which resulted in a dozen deaths in the state, among the more than 30 heat-related fatalities across four states. Other forecast offices from the Mid-Atlantic to New England are warning that several days of dangerous heat and unusually warm nights will create a heightened risk of heat-related illness.

Richmond, Virginia, is forecast to top 100 degrees for three consecutive days, potentially breaking daily records each day while approaching the city’s hottest July temperatures on record.

In North Carolina, Raleigh isn’t expected to challenge its all-time high temperature record of 106 degrees, but overnight lows late this week could flirt with the city’s all-time warm overnight low record of 80 degrees.

In Washington, DC, highs of 102 degrees Thursday and 103 degrees Friday would break daily records if the forecast verifies, while overnight temperatures could remain above 80 degrees, threatening record warm lows. New York City could tie both its daily high temperature record Thursday and its record warm overnight low Thursday night.

The coming heat wave will also have a massive reach. More than 100 million people are in a Level 3 of 4 “major” or Level 4 of 4 “extreme” heat risk from the Deep South to as far north as parts of Minnesota, Wisconsin, Michigan and Maine, and as far east as New York and Boston on one or more day this week, according to the National Weather Service.

Heat this severe can affect anyone without proper cooling or hydration, according to the weather service. Little relief is expected at night as high humidity keeps temperatures elevated and prevents sweat from evaporating efficiently, making it harder for the body to cool itself.

Low temperatures this week won’t fall below the lower-to-middle 70s in the Midwest and Great Lakes. Urban areas, where concrete and asphalt absorb heat during the day and slowly release it overnight, could struggle to fall much below 80 degrees.

Prolonged exposure to extreme heat can cause illnesses like heat exhaustion, heat cramps, and the most serious type, heat stroke, according to the US Centers for Disease Control and Prevention. Emergency room visits for heat-related illness surge on “major” and “extreme” risk days, according to the National Weather Service.

The heat wave is expected to peak during one of the busiest travel and outdoor celebration periods of the year. Millions of Americans attending parades, cookouts, sporting events and Fourth of July fireworks should prepare for dangerous heat, particularly during the afternoon and early evening hours.

Parts of the Midwest and Northeast will see temperatures ease later in the holiday weekend as the upper-level ridge of high pressure weakens and shifts westward, allowing thunderstorms to develop. But above-average temperatures are expected to persist across much of the South into the following week.

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Meteorologist Chris Dolce contributed to this report.