This weekend, one of Portland's most successful hip-hop nights celebrates its first birthday.

It's called Thorn City Improv--ever heard of it?

Didn't think so.

It's not like the weekly event, hosted in part by the local, live hip-hop band the Chosen, exists in the underground. Case in three points: Thorn City's promo fliers and handouts make their way across Portland, into bars and record stores, and onto telephone poles every week like clockwork. Frequent Thorn City guests Madgesdiq, Onry Ozzborn and Mic Crenshaw are no mere blips on Portland's musical radar. And its location, the Ash Street Saloon, can't be called a no man's land (though it is better-known for its dirty, punk-rock persona).

Despite the lack of a nightlife buzz, Thorn City's approaching one-year anniversary indicates that bodies are filling the space. Add the fact that some of the biggest names on the scene have stopped in at some point to say hello and take the stage, and it appears a new home base for Stumptown rappers and rhymers has arrived.

On a recent visit, the Ash Street's main room wasn't so much full but filling up--though this (somewhat dismal) attendance seems the fault of the weekday on which it falls: Tuesday. Despite the unfortunate calendar designation, the high-fiving and backslapping on this night indicates that Thorn City's crew of regulars not only includes its players on stage but members of the audience as well. And that crowd, on this night, is a diverse group in which black and white, Latino and Asian fans gather for a listen--it's a rare and welcome sight 'round downtown's largely white nightlife population.

As for the talent on stage, the rotating lineups, live hip-hop band and "improv" format provide a broad palette from which artists can paint impromptu lyrical portraits and then meet like-minded others.

On the same night, a traveling group from Arizona, the Drunken Immortals, takes the stage for a few rounds of hard-hitting, politically minded rapping. Though they claim to be on a Northwest tour, the vibe feels more like friends stopping in for a spell than a featured act.

On Saturday, the Thorn City crew celebrates one year of fostering a scene and making new friends in the hip-hop community. With this primetime weekend slot, they might even make a few more.

Thorn City Improv turns 1 year old Saturday, Nov. 7. Ash Street Saloon, 225 SW Ash St., 226-0430. Catch regular shows 9:30 pm Tuesdays. $5. 21+.