Cities around the country have teed up their biggest, baddest fireworks displays to ring in America’s 250th birthday Saturday — including a record-breaking Macy’s show that will shoot off from two New York City rivers.

But a monster heat dome could mean less-than-splendid viewing conditions for the Big Apple and other East Coast cities.

Humid, moist air tends to scatter and absorb light from fireworks, warned Accuweather meteorologist Carl Erickson.

“It can make the fireworks look a little less crisp, less vibrant,” he told The Post.

New York is expected to be around 80 degrees and 75% humidity on Saturday night — soupy weather for an otherwise spectacular show.

Worse, low forecasted winds mean smoke and pollution could hang in the sky, creating a layer of haze between the bombs bursting in air and the spectators below.

Potential storms forecasted for New York and other northeastern cities could wash away the haze and cool things down.

“But you still have that humidity,” Erickson noted.

Still, the industry is undaunted as pyrotechnics companies pull out all the stops for the semiquincentennial. The display in Washington, DC, is expected to set a world record for the biggest ever — with 851,000 shells popping off Saturday night.

“This year every show across the nation [is] going to be bigger, badder, and more elaborate because it’s America’s 250th. This is a special time,” said Julie Heckman, director for the American Pyrotechnics Association.

Display operators spend weeks monitoring the weather and watch the skies minute-by-minute on the day of the show — ready to launch even in pouring rain, she said.

Barring strong wind or lightning, there will be fire in the skies — humidity be damned.

Whatever the weather, this is the year to come out for fireworks, Heckman said.

Big commercial displays took off in 1976 for the last major centennial celebration.

Fifty years later, display companies are bursting to show off the latest in pyrotechnics, like computer-powered choreography, drone integration, and, of course, bigger booms.

As for what they’ll actually look like, modern displays favor pastel colors like pinks, coral, and chartreuse.

“But this Fourth of July, it’s all gonna be red, white, and blue,” Heckman said.