* Smaller venue will disrupt final night of convention
* Tens of thousands of supporters will be left out
* Clinton in spotlight at convention on Wednesday
CHARLOTTE, N.C., Sept 5 (Reuters) - Severe weather forecasts put a crimp on U.S. President Barack Obama's nomination party on Wednesday, forcing him to move his planned acceptance speech from a 74,000-seat outdoor football stadium to a much smaller indoor arena.
The shift to the approximately 20,000-seat Time Warner Cable Arena was a setback for Obama, who hoped to create a visual spectacle in Charlotte's Bank of America stadium to rival his 2008 acceptance speech in a football stadium in Denver.
Tickets had been distributed to tens of thousands of Obama supporters from around the country who planned to converge on Charlotte to hear the biggest speech in his campaign for the Nov. 6 election against Republican rival Mitt Romney.
Obama will speak to those supporters on a conference call on Thursday afternoon, organizers said.
Weather forecasters had predicted a chance of thunderstorms on Thursday night in Charlotte, which has experienced heavy evening rains for the last few days.
"We have been monitoring weather forecasts closely and several reports predict thunderstorms in the area," convention chief Steve Kerrigan said in a statement.
"Therefore we have decided to move Thursday's proceedings to Time Warner Cable Arena to ensure the safety and security of our delegates and convention guests."
James Mitchell, 45, a Michigan delegate, said he expected officials would make alternative plans for the tens of thousands of volunteers and others who will be turned away from the indoor arena on Thursday.
"They may still be able to accommodate them - it's just going to be a madhouse," said Mitchell, who works for a market research firm in Detroit. But he said there were advantages to a smaller venue.
"I think it's going to be electrifying," he said. "Sometimes smaller venues create an energy and an intensity that is going to be over the top."
Tropical Storm Isaac also disrupted Romney's Republican nominating convention last week in Florida, forcing him to cancel one day of the planned four-day gathering.
The Democrats' convention started on Tuesday, with an impassioned speech by first lady Michelle Obama who called on voters to give her husband another term even though the change he promised in his 2008 campaign has been slow to come.
Former President Bill Clinton will take the spotlight for Democrats on the convention's second day on Wednesday, aiming to build on the momentum of a fired-up first night with a reminder to voters of the economic good times he led in the White House.
The appearance by Clinton, perhaps the party's most popular elder statesmen but a sometimes uneasy ally of Obama, highlights a night that concludes in the late hours with Obama's nomination for a second term.
"He's going to make the case for Barack Obama," Chicago Mayor Rahm Emanuel, Obama's former chief of staff and a former Clinton aide, told CBS's "This Morning."
He said Clinton will remind voters of "who we are as a party and why that matters to the middle class and people who are struggling." The two share the "same values, same policies, same goals," Emanuel said.
Clinton's high approval ratings, and voter nostalgia for the budget surpluses and job growth he produced during two terms as president in the 1990s, have made him a valuable asset for Obama despite a sometimes rocky relationship after Obama's bitter 2008 primary battle with Clinton's wife, former first lady Hillary Clinton.
Clinton, who will be speaking at his seventh consecutive convention since his debut in 1988, already has appeared in an ad for Obama.
The convention schedule on Wednesday also includes a featured slot for Elizabeth Warren, the U.S. Senate candidate from Massachusetts, and U.S. Representative Barney Frank.