On a squat checkerboard stage, in front of a full house in a tucked-away Mesa storefront theater, four young Valley improvisational actors are pretending they’re making a televised advice program.

Yousef Hawash, playing the show’s host, takes on an exaggerated Spanish accent — sort of “Scarface’s” Tony Montana, were he to host daytime TV — and makes his ad-lib introduction.

“Hello, my freends, and welcome to the Telemundo broadcast of ‘We Do What You Want Us to Do When You Ask Us to Do It,’ ” he says, to titters from the crowd. Then, a killer punch line: “In Spanish it’s, like, two words. I’m sorry.”

The crowd erupts in laughter.

OK, so you kind of had to be there. That’s the problem with improv comedy. Like Mad Libs, it’s an off-the-cuff audience participation riff that can leave a group’s sides in stitches, even if it doesn’t exactly translate later. It’s all about experiencing the moment.

This moment, it seems, the Valley is experiencing an improv boom. Two months ago, Dorian Lenz, 29, and his wife, Krissy, 27, opened a Phoenix chapter of the National Comedy Theatre, which stages 90-minute competitive improv games in the west Mesa storefront that used to be the funky coffeehouse and performance space Undici Undici. (Dorian, who grew up in Chandler, is a Valley improv vet who recalls performing at Undici. He now works days as a stockbroker, while Krissy raises their 2-year-old daughter, Zoe. Dorian’s parents run the nearby Mesa sandwich shop Cheba Hut.)

Their 99-seat theater joins several improv troupes that have sprouted up across the Valley in recent years.

Meanwhile, this weekend finds the city-sponsored Phoenix Improv Festival going strong in its seventh season, playing for the first time at the downtown Herberger Theater Center. Many of the Valley’s top acts, plus visiting troupes like “The Daily Show” correspondent Dan Bakkedahl’s Hollywood troupe Zumpf and Chicago’s T.J. & Pete, aka T.J. Jagodowski and Peter Grosz, who filmed commercials for Sonic Drive-Ins.

For audiences at Mesa’s National Comedy Theatre, the appeal is in its family-friendly nature: Part of the rules, as explained by a referee/emcee, is that any offensive language — by a performer or audience member — earns a “brown bag foul,” and the person must wear a brown paper bag over his or her head as penalty.

Chandler’s John Ronan, 43, brought his wife and friends to a recent Saturday night show at National Comedy Theatre. They wanted comedy, he explained, but not the adult language they might get at a comedy club.

“Here,” he said, “it’s clean and improvisational and just as funny.”

Stacey Reed, a volunteer coordinator for the Phoenix Improv Festival, moved from New York to the Valley three years ago. There, she says, the improvisational scene was well-established. Here, she’s witnessing a kind of groundswell.

“It’s really neat to be a part of it here,” she says, “because you can see it growing by leaps and bounds every year.”

The joy of improv, Reed says, is its ephemeral nature: “It’s a unique experience. Every time you go to a show, it will be different. You’re watching performers come up with something on the spot.”