As clouds swirled over dress rehearsal for PBS’s “A Capitol Fourth” on Sunday morning on the West Lawn of the U.S. Capitol, host Tom Bergeron couldn’t help but throw in a few jokes about the weather as he practiced his lines via teleprompter.

“Thunder, lightning and torrential downpours!” Bergeron said on stage as he reeled off what audiences could expect during PBS’s annual Fourth of July fireworks and concert special. Later, he added, “We’ve only had six tornado warnings.” Although there were laughs all around, would Bergeron panic if he woke up Monday morning for the actual show and saw a gray sky?

“Oh, no,” he told us backstage. He’s not worried about potential rain. “The first rule of improv, as I was taught it, is you say yes to everything. You don’t tense up. … I’m open for anything. That doesn’t bother me.”

Of course, it helps that Bergeron has seen basically everything in his decades as an Emmy-winning TV host, from “Hollywood Squares” to “America’s Funniest Home Videos.” He’s especially unfazed when it comes to live television, given that he has co-hosted ABC’s hit reality competition show “Dancing With the Stars” since 2005, and that’s always a frenzied couple of hours.

So even though “A Capitol Fourth” (airing on PBS at 8 p.m., live-streamed on PBS.org and Facebook Live) is on a tight schedule, packed with performances from Smokey Robinson,  Kenny Loggins, Sutton Foster, Yolanda Williams, Cassadee Pope and Christopher Jackson, you can expect some of Bergeron’s signature ad-libs between proceedings. He’s especially jazzed to meet Jackson, who plays George Washington in the smash musical “Hamilton”; Bergeron saw the show last month and loved it, although he quipped during rehearsal that he had to take out a second mortgage to afford tickets.

And is Bergeron especially eager to have the best seat in the house for the fireworks, with his prime perch on the West Lawn?

“To be honest with you, the fireworks — even though that gets such attention — is the least interesting part of it to me. I love that first moment walking out on the stage, seeing all the people, seeing the Capitol building … and there’s all the incredible talent,” Bergeron said. “Fireworks, they’re nice, but I’ve seen a lot of fireworks. Sorry, that’s not what gets me here. Everything else gets me here.”