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By Elisha Fieldstadt

The "heat dome" has some Americans longing for the spine-shivering days of the polar vortex.

On Saturday, the dome — a ridge of high pressure that traps hot air for an extended period of time — had 110 million Americans under heat advisories, warnings or watches after many had already suffered through two days of the sweltering conditions.

Related: What is a 'Heat Dome'? Everything You Need to Know

Washington was the only state of the lower 48 on Friday spared from having some portion hit by at least 90 degree temperatures.

But it's the heat index — the "feels like" temperature when heat is paired with humidity — that created health risks on Friday and continued to be a threat through the weekend.

Heat indices were expected to linger between 100 and 110 degrees across the country on Saturday and Sunday, according to

The Northeast will feel the hottest over the weekend, and officials in many major cities are taking precautions.

Meanwhile, utility companies in the region, including Con Edison and Pepco, were asking residents to reserve power so that much-needed air conditioners wouldn't fail.

A man cools off himself in a fountain during a heat wave in New York City on July 23, 2016.EDUARDO MUNOZ / Reuters

If Washington, D.C., hits 100 degrees this weekend — as expected — it would be the first time since 2012.

Officials there issued a heat emergency, and the Washington Nationals were taking steps to keep their fans safe, like letting them bring two bottles of water into the stadium, according to NBC Washington.

A heat emergency was also issued in Boston.

Philadelphia is expected to climb to 98 degrees on Saturday — a high the city hasn't seen in three years.

Cooling centers were set up across New York City, where residents had to sweat through the hottest day there all year on Friday, when the mercury in Central Park boiled to 94 degrees.

According to the National Oceanic and Atmospheric Administration (NOAA), the widespread heat wave is especially dangerous because lows at night will hardly dip below 80, depriving Americans from relief from the "oppressive" heat.

Excessive heat has killed more Americans in the past decade — an average of more than 100 people per year — than any other weather event, according to the National Weather Service, which recommends staying hydrated and limiting outdoor activities.

The advice will need to be heeded until Tuesday, when the heat wave is finally expected to let up in most states, according to NOAA. But the Southeast won't likely see relief until Thursday.

Full relief, in the form of autumn temperatures, likely won't come for a few months however. NOAA predicts above-average temperatures across the U.S. straight through October.

While the current heat wave hasn't been attributed to global warming, climate scientist Dan Collins told The Associated Press that it has been a factor in many recent extended periods of high heat.

And there have been more hot days than usual. June marked 14 consecutive months of record heat around the world, according to NOAA.