The severe weather that spawned deadly tornadoes throughout the US South threatened to delay Thursday's planned launch of shuttle Atlantis, already two months late in getting to the space station with a new lab. Rain, clouds and possibly even a fierce thunderstorm were expected right around 2:45 p.m., launch time, prompting forecasters to reduce the odds of an on-time liftoff to a mere 30 percent. NASA managers said they would not consider canceling the launch for weather reasons until early Thursday, if at all. Although the weather should improve Friday, it is not expected to get significantly better until early next week, shuttle weather officer Kathy Winters said. Atlantis has been sitting on the launch pad, with the European Space Agency's Columbus lab tucked in its payload bay, since late last year. Two back-to-back launch attempts fizzled in December because of fuel gauge failures, the same kind of problem that had bedeviled the shuttle program for more than two years. Atlantis' seven astronauts - five Americans, one German and one Frenchman - will install the $2 billion Columbus lab at the international space station, already home to the US lab Destiny. The Japanese Space Agency's lab Kibo, or Hope, will follow Columbus to the space station in pieces on three separate shuttle flights.