Meteorologists have given a mere 30% chance of acceptable weather conditions for the launch, set for 2:45 p.m. (7:45 p.m. GMT). Nearby Arkansas, Kentucky and Alabama have been hit by major tornadoes in the last few days that have killed at least 52 people.
"The good news for Atlantis and its crew of seven astronauts is that the shuttle is showing no technical issues and liftoff preparations are continuing at the launch pad and in the launch team facilities," NASA said.
The crew consists of five U.S. astronauts, one Frenchman, and one German.
The launch of the Atlantis, which is set to put into orbit Europe's first space lab, was aborted twice in December last year due to engine problems.
The shuttle is set to deliver the European Space Agency's $2 billion Columbus module to the International Space Station.
