U.S. President Barack Obama has cancelled plans for an outdoor convention speech and has moved the Democratic convention's final night inside, citing the possibility of severe weather.

Obama had planned to accept his party's nomination in an outdoor football stadium before a crowd of up to 74,000 people. But Obama officials said forecasters have predicted severe thunderstorms Thursday in the 9 p.m. to 10 p.m. hour, raising concerns about the safety of supporters, volunteers, staff members and law enforcement.

Officials said Thursday's entire program would be moved indoors, including Vice President Joe Biden's speech. The events will be held at the Time Warner Cable Arena, the site of the first two days of the convention proceedings.

Obama will speak to about 15,000 people gathered in the arena Thursday, a far smaller audience than had been expected at the outdoor stadium.

Democrats were warily watching the weather all week. Their worst case scenario was a last-minute cancellation that would strand tens of thousands of people, many of whom had planned to arrive by the busload in the middle of the storm with no place to go.

Obama's team, locked in a tight race with Republican Mitt Romney in this Southern battleground state, determined that wasn't worth the political risk.

Democrats were also worried about the possibility of anti-Obama hecklers acquiring some of the free tickets to the event and disrupting the president's speech. The move indoors limits that possibility because most of those in the crowd will be official convention participants.

Opponents charge lack of enthusiasm

Republicans, who cancelled the first day of their convention due to weather in Tampa, Fla., accused Democrats of downgrading their events because of low enthusiasm.

"After promising to hold the event at Bank of America stadium rain or shine, suddenly Team Obama is moving inside after questions about enthusiasm for the event," said Kirsten Kukowski, spokeswoman for the Republican National Committee. "What's the real forecast for the speech? Forty per cent chance of lies and scattered excuses."

Democrats insisted the decision was based strictly on the weather.

'What's the real forecast for the speech? Forty per cent chance of lies and scattered excuses.'—Republican National Committee spokesperson Kirsten Kukowski

Steve Kerrigan, who heads the Democratic convention, said more than 65,000 people had signed up for credentials to attend the outdoor speech but now could not be accommodated because of the smaller venue. He said organizers were encouraging those credential holders and "Americans across the country to continue to come together with their friends and neighbors to watch and participate in history."

Kerrigan said Obama would speak to those credential holders on a national conference call Thursday afternoon. "We will work with the campaign to ensure that those unable to attend tomorrow's event will be invited to see the president between now and Election Day," he said.

The president arrived in Charlotte on Wednesday afternoon. His departure from Washington was slightly delayed by a thunderstorm.

Forecasts for Thursday night in Charlotte had been improving all through the week. The National Weather Service said Wednesday morning that there is a 40 per cent chance of thunderstorms in the afternoon, but it would drop to 20 per cent by the time the president was scheduled to speak in the 10 p.m. hour.

But there was still no guarantee of good weather for Obama's speech.

"We're dealing with a warm, unstable air mass, so you can never absolutely say it's not going to rain or storm," said National Weather Service meteorologist Bryan McAvoy.

Days of wet weather

It has rained every day since Saturday in Charlotte. Strong storms brought downpours of nearly an inch Monday and Tuesday.

Jan Bauer, a delegate from Ames, Iowa, said she was thrilled about the move `because it's not very comfortable sitting in the rain."

The move also helps Obama avoid comparisons to 2008, when he accepted the Democratic nomination before a capacity crowd of 84,000 people at an outdoor football stadium in Denver. Democrats had been fretting for months that the president might not be able to fill the slightly smaller stadium this time around.

Obama's campaign had planned to use the larger public rally as an opportunity to boost voter registration and recruit new volunteers. Those efforts will be hampered by the move indoors, but the campaign still has voter information from the 65,000 people who signed up for credentials.

The venue switch is sure to be a costly letdown, if the 2008 Democratic convention is any guide.

Charlotte convention organizers have been guarded about their expenses and won't have to publicly report them until October. Federal campaign records from the Democratic convention in Denver show that the host committee spent more than $760,000 just to rent the outdoor stadium, not counting all the costs of outfitting it for Obama's acceptance speech.

The dual venues also doubled the cost of covering the Charlotte convention for most news organizations.