The 45th Weather Squadron from Patrick Air Force Base is predicting a 30% chance that weather will delay the Shuttle launch scheduled at Kennedy Space Center for 7:55 EST Friday evening.  The astronauts on the STS-126 mission will transport equipment to expand the International Space Station to accomodate a crew of six.

According to NASA’s Oct. 1 press release, “Endeavour will carry a reusable logistics that will hold supplies and equipment, including additional crew quarters, a second treadmill, equipment for the regenerative life support system and spare hardware.”

However, the concerns for Friday are thick clouds and possible rain showers within 20 miles.  If the launch is delayed, the conditions are only expected to get worse.  The 45th Squadron expects a 70% probability of scrubbing a Saturday launch.  Should the launch be delayed twice, Sunday’s improving forecast lowers the postponement probability to 20%.

NASA also monitors weather conditions at the primary emergency landing sites.   Conditions are good at California’s Edwards Air Force Base and the White Sands Missile Range site in New Mexico.  Two of the three Transatlantic landing sites —  the Istres Air Base in France, and Zaragoza in Spain, may have marginal conditions should they be needed for an emergency landing — something that’s never happened in the history of the Shuttle program.

Miles O’Brien will cover the launch live Friday night at 7:55pm on CNN and CNN International.

Jamie Burns, CNN Weather