See the top cities in danger of shattering Fourth of July records as extreme heat dome descends on nation

A massive heat dome is settling over the eastern half of the country, triggering the first major heat wave of the summer, just ahead of the July 4 holiday.

While temperatures may peak before July 4 itself, more than 44 million people across the country will still experience triple-digit air temperatures or heat index values as they celebrate America's 250th birthday.

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More than 20 states are expected to reach 100 degrees this week and over 230 million people will surpass 90 degrees, with more than 140 municipalities expected to see record-high temperatures.

Some wore sweaters in Washington, D.C., for the opening weekend of the Great American State Fair on the National Mall. But those attending on July 4 will need plenty of sunscreen and water.

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While it will feel like a desert across much of the Central and Eastern U.S. on Independence Day, the Desert Southwest will still officially hold the hottest July 4 temperatures this weekend.

Bullhead City and Lake Havasu City, Arizona, along with a few California municipalities are expected to be the hottest cities this July 4, with temperatures reaching a scorching high of 107 degrees.

Fortunately, there should be some relief from the heat at night along the Colorado River, where Bullhead City is expected to host its 36th annual Independence Day fireworks show.

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Phoenix, Goodyear and Luke, Arizona, will not be far behind with an expected high temperature of 106 degrees.

Calexico, Blythe and Needles, California, are also forecast to reach 107 degrees, in Imperial, Riverside and San Bernardino counties respectively.

The Calexico Recreation Department is helping families cool off and celebrate America 250 with a family night at the local aquatic center.

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Imperial and Thermal, California, are set to reach 106 degrees on the Fourth.

Intense heat will remain across much of the Southern Plains through the holiday weekend, with Oklahoma City forecast to reach the century mark on July 4.

OKC will be holding Independence Day celebrations at OKANA Indoor Waterpark & Resort in addition to the city's fireworks show.

Dallas is forecast to join Oklahoma City with triple-digit temperatures on July 4th.

Those attending America 250 celebrations downtown or lining up for the historic Lakewood Fourth of July Parade and festival should be sure to pack plenty of water.

JULY 4TH FORECAST OUTLOOK: WHAT WILL THE WEATHER LOOK LIKE ACROSS THE US FOR AMERICA'S 250TH BIRTHDAY?

Philadelphia has already opened cooling stations ahead of July 4, where it is forecast to hit 100 degrees.

The city is a centerpiece for America 250 celebrations, featuring a morning ceremony at Independence Hall and a massive concert on the Benjamin Franklin Parkway beginning at 5 p.m.

In addition, afternoon thunderstorms could provide some heat relief, but could be strong enough to disrupt outdoor activities.

The nation's capital is currently forecast to stay just under the century mark, but afternoon thunderstorms are also possible.

Those visiting the Great American State Fair or attending the National Independence Day Parade in the morning, or the Capitol Fourth Concert in the evening, should monitor the forecast throughout the week.

While New York City is expected to see back-to-back days of 100 degrees for the first time since 2011, July 4 itself will be slightly cooler, with thunderstorms possible ahead of the dual milestone of the 50th Annual Macy's 4th of July Fireworks and America 250.