This holiday forecast blows!

Thanksgiving paradegoers should bundle up for the coldest temperatures in 20 years — and brace for powerful winds that threaten to ground dazzling giant balloons.

It’s expected to plunge into the low 20s in Manhattan — but it will feel more like the teens — in the coldest projected Thanksgiving on record since 1996, meteorologists told The Post.

“It’s going to be brutal out there,” said Accuweather senior meteorologist Dave Dombek. “It’s going to be cold. Very, very cold.”

He added, “If things stay as is, this will be the third-coldest Thanksgiving in New York history” — with the most frigid reaching a low of 19 degrees in 1901.

Sustained wind could reach up to 25 mph and gusts could blow up to 35 mph, which would ground beloved balloons such as Charlie Brown, the Grinch and SpongeBob SquarePants.

If sustained winds exceed 23 mph and gusts surpass 34 mph, none of this year’s 16 character balloons will be allowed to soar due to city regulations, Macy’s Thanksgiving Day Parade spokesman Orlando Veras told The Post.

It would be the first time the city has grounded the colorful balloons since 1971. In 1997, a woman was left in a coma when a powerful gust of wind caused the Cat in the Hat balloon to strike a streetlight, which fell and hit her head.

But organizers haven’t yet made a call about whether to ground the balloons this year.

“It is too early to make any determinations as to the flight of the balloons,” Veras said Monday.

“In the morning, just prior to the start of the event, Macy’s and the NYPD will make a final determination on the flight of the giant balloons, based on the current weather data available from the parade route and a number of additional sources.”

Overall, Thursday’s low temperature is expected to be 21 degrees with a wind chill factor of 10 to 16 degrees, Dombek said.

New floats this year include Elf on the Shelf, Rise of the Teenage Mutant Ninja Turtles, Splashing Safari Adventure by Kalahari Resorts and Conventions, and Fantasy Chocolate Factory by Kinder. Oldies but goodies include the Pillsbury Doughboy, the Grinch and Ronald McDonald.