By Eric Johnson
CHARLOTTE, North Carolina (Reuters) - Democrats in Charlotte, North Carolina, have one eye on the sky as bad weather threatens to spoil the biggest speech of President Barack Obama's re-election campaign.
Meteorologists are forecasting possible thunderstorms over Charlotte for Thursday, when Obama is due to address a crowd of up to 74,000 in a football stadium at the end of the Democratic National Convention.
It was the second time in a week that Mother Nature put a party convention in jeopardy after Tropical Storm Isaac forced the Republicans to cancel the first day of their gathering in Tampa.
While the chances of storms in Charlotte are only about one-in-three, the thought of disruption to Obama's signature event because of the danger of lightning has convention organizers in a sweat.
Tens of thousands of Obama supporters from around the country could be left out in the cold with little hope of taking part in the convention festivities that will launch Obama into the final leg of the campaign for the November 6 election.
Ironically, the bad weather is a leftover from Isaac, which spared Tampa but then became a hurricane and slammed into Louisiana.
"It is just a really moist air mass" that has moved northeast after Isaac, said National Weather Service meteorologist Brian Hoeth.
Thunderstorms could blanket parts of the Charlotte area with roughly a quarter-inch or more of rain on Tuesday and Wednesday, Hoeth said. Storms are less likely on Thursday but are projected to be stronger.
The National Weather Service predicts a 30 percent chance of thunderstorms in Charlotte on Thursday night, when Obama is due to give his nomination acceptance speech at the Bank of America stadium after 10 p.m. eastern time.
The likelihood of thunderstorms then would be a huge headache for the convention planners.
Obama's speech could be delayed for a few hours or brought forward, but that would play havoc with TV network schedules and possibly bump the address from prime time just as the Democrat needs as much exposure as possible in his fight with Republican rival Mitt Romney for the White House.
The Democrats could relocate the speech from the football stadium, home to the NFL's Carolina Panthers, to Charlotte's Time Warner Cable Arena, where most of the convention is being held this week.
But that indoor site only holds some 19,000 people, potentially leaving more than 50,000 Obama supporters with nowhere to go on Thursday night.
A venue change would also mean a less dramatic backdrop for Obama's appeal to voters to give him four more years to turn around the economy.
"Theatrics I can do without, but I wouldn't want to be excluded, having come all the way from California," said Tawnie Farmer, 69, a big Obama campaign donor.
Organizers have a well-laid plan for bad weather, said convention committee spokeswoman Joanne Peters.
"If we have to activate a contingency plan due to severe weather, we will make a determination with enough time for arrangements to be made," Peters said in a statement.
The details of their plan are not being released to avoid confusing supporters, a Democratic official said.
(Editing by Alistair Bell and Alden Bentley)