SPRINGFIELD - Just as U.S. Sen. Barack Obama used the backdrop of Illinois' Old State Capitol to kick off his successful primary campaign for president, he's using the Springfield landmark as the unofficial launching pad for his general election bid.

Eighteen months after he stood before an estimated 15,000 frigid people to announce his presidential aspirations, Obama will kick off his trip to the Democratic National Convention on Saturday with a speech at the same site.

He could be accompanied by his vice presidential pick, which is expected to be announced any day.

Although a set time for the event wasn't known Wednesday, attendees are encouraged to arrive at the site by noon Saturday. The public entrance is on Washington Street at 7th Street in downtown Springfield.

Analysts say Obama's return to Springfield is a symbolic way of bringing the Obama campaign full circle.

"I think it provides very nice symmetry for the campaign," said Millikin University political scientist Mark Wrighton.

The event will serve as the first of several stops in states that will likely be more competitive than Illinois for Obama and his opponent, Republican John McCain. The tour will precede Obama's arrival at the Democratic National Convention, which begins Monday in Denver.

The Old State Capitol is the same place where Abraham Lincoln, the nation's 16th president, delivered his "House Divided" speech 150 years ago.

Obama's 20-minute speech back in February 2007 used many of the same touchstones he employed in his drive to the top of the Democratic ticket. He talked about change, health care and a pullout of troops from Iraq.

Not only has Obama's stock in the presidential sweepstakes risen since his last visit to Springfield, but the temperatures will be a bit warmer.

While an estimated 15,000 people shivered through the festivities in 12-degree weather back then, temperatures are supposed to be in the high 80s Saturday.

Wrighton said the crowd could be bigger this time around.

"Not only will it be warmer, but more people may have warmed up to him," Wrighton said.

The forecast does call for a slight chance of thunderstorms.