Mission managers met Wednesday afternoon and into the evening to discuss an electrical problem that forced a one-day delay for Discovery's final voyage. They concluded the shuttle is safe to fly.
But forecasters say there is an 80 percent chance that thunderstorms will keep Discovery on the pad. Liftoff is scheduled for 3:29 p.m.
Managers will reconvene before daybreak to assess the weather situation, before loading the shuttle's fuel tank.
Discovery's flight to the International Space Station was stalled last week by gas leaks. Then a problem cropped up Tuesday with a computerized controller for one of the main engines. At this point, the mission is running three days late.