Storms may wash out last space shuttle launch Fri.

Space shuttle Atlantis glides by rescue vehicles before landing on Kennedy Space Center's runway 33 Wednesday, May 26, 2010 in Cape Canaveral, Fla. (Terry Renna)

July 5, 2011 6:11:21 PM PDT
The countdown is under way for the last space shuttle launch.

But forecasters say it could be delayed. A shuttle weather officer says there's a 60 percent chance that rain or thunderstorms will postpone Friday's liftoff of Atlantis.

After that, the weather improves with each passing day. The four astronauts assigned to the 12-day flight arrived at Kennedy Space Center yesterday.

Atlantis is making one final supply run to the International Space Station before retiring. As many as a million spectators are expected to jam the Cape Canaveral area for the historic send-off.