Pleasant weather welcomed the crowds Saturday afternoon at Bumbershoot 2011. When evening rolled around, the headline acts kicked in.

Saturday evening update: At its best, Bumbershoot is a source of new discoveries and an encounter with longtime favorites.

This year there were several discoveries for me on Saturday.

First, there was young Caleb Klauder, a baby-faced Portland country musician who rekindles the spirit of the old-time honky-tonk. Raised in Georgia by way of Orcas Island, Klauder is a fine mandolin picker, and his band has those classic pedal steel guitar and fiddle riffs down. Klauder’s pleasingly reedy vocals channel the Hank Williams generation, and his repertoire — sweet-tempered tunes of his own, and classics like Dolly Parton’s “Rockin’ Years” — is mighty tasty.

In another vein entirely: The MarchFourth Marching Band, another Portland outfit. Picture this: a demented, jazzed-up drum-and-bugle-corps version of Pink Martini with a pinch of Cirque du Soleil, featuring hoop-twirlers, brass beboppers and stiltwalking acrobats who mosh. This tribe is a carnival and a party, and they got everybody grooving and grinning.

And how good to be introduced to Vusi Mahlesela, a soulful, politically engaged South African guitarist, singer and songwriter, who managed to communicate his concerns and his joy in the vastness of KeyArena, when a more intimate venue would have suited him better. A longtime activist who performed at Nelson Mandela’s inauguration, Mahlesela offered tunes from his new album, “Say Africa” (produced by Taj Mahal), including an exuberant ode in praise of strong, resilient women.

And closing out Saturday’s musical offerings was someone I can never get enough of: the great songstress Mavis Staples. The preaching and teaching Mavis, and her sizzling band and back-up singers, were in fine form. They lifted spirits with a capella gospel numbers, civil-rights anthems and signature performances of tunes like “The Weight” and “Have a Little Faith.” What a satisfying way to end a long day at Bumbershoot.

Earlier in the day: Weather can be a make-or-break factor for the annual Labor Day weekend Bumbershoot music and arts festival. This year, the weather was made to order.

Bright and clear, with a comfortable light breeze, on Saturday the climate was just about perfect for a Seattle late-summer afternoon.

It helped draw a good-sized crowd to Bumbershoot, though not a record one — perhaps because of the fest’s emphasis on Saturday on upcoming pop-folk and roots musicians, with fewer big headliners than in some Bumbershoots past.

That allowed plenty of room for attendees (which looked to be all-ages crowd) to maneuver, and to stroll from stage to stage taking in bands and other acts like the pleasing young country singer-songwriter Caleb Klauder, of Portland, or the hot, Boise-based dance company the Trey McIntyre Project.

But many seemed to be having fun just lollygagging and people-watching.

Asked about the flow of paying customers at her jewelry booth, Jodi Baarstad (a 20-year Bumbershoot vendor) said, “It’s not like the glory years. The economy has slowed down everything over the past five years. But it’s sunny, which makes everything better.”

New and repeat visitors to Bumbershoot took awhile to orient themselves on the grounds of Seattle Center, which is in the midst of a partial makeover in honor of its 50th anniversary.

Several areas of the Center that used to host Bumbershoot events are now blocked off as construction sites. And the locations of food and craft booths, art exhibits and music venues have been reshuffled.

The largest food area is now the newly named Center Square, a paved, open area bordered by the Space Needle, the monorail station, EMP and Center House.

And the most striking programming change is a venue switch for the biggest-name musical acts. Instead of being presented at the funky, outdoor Memorial Stadium, as they have been in recent years, they’ve been moved indoors to the KeyArena.

That didn’t deter fans of The Presidents of the United States of America, who smoothly streamed into the Key and filled the standing-only floor and many of the seats. The three-man Seattle band was in fine form as it rocked out to fan faves like the zany “Kitty.” And the amplified sound was much sharper and more balanced than the average Memorial Stadium concert of yore.

Not everyone appreciated the shift. “It’s fine, I guess, but I miss the open-air feeling of the stadium,” said Ryan Smith, of Everett.

His friend Mike Morgan, of Lake Stevens, disagreed. “It’s kind of cool just walking in and out of the Key whenever you feel like it. That’s a new experience for me.”

Bumbershoot continues through Labor Day.

Misha Berson: mberson@seattletimes.com