11:38 update: Congratulations NASA. Atlantis, traveling at a speed of more 15,000 mph, has exited the Earth’s atmosphere and powered flight is no longer needed. After a “flawless launch”, the main engines have been cutoff and Atlantis is “off the tank”. Atlantis has begun its final orbit.
11:29 update: Atlantis lifts off amidst a mix of clouds and sun.
11:28 update: Count clockdown resuming.
11:27 update: Hold being cleared.
11:26 update: HOLD.
11:25 update: T-1 minute.
11:22 update: T-4 minutes until launch. Watch launch live at this link.
11:14 update: Shuttle Launch Control: “Launch weather has no constraints to launch” ... “We are ready to proceed with launch at this time...” “Chances of thundershowers very low”
11:10 update: NASA official just said via Shuttle Launch Control: “We knew weather would present a challenge. We’re increasing our optimism. ... Currently we’re watching some clouds at the 12,000 foot levels that are building and moving toward the launch area.”
11:00 a.m. update: Latest satellite and radar continue to look OK but there are a couple showers developing to the south that bear watching. The NASA announcer just said “weather looks reasonably stable... don’t see any buildups.” But he cautioned “the Space Flight meteorology group says there are number of factors they have to consider ... and then they will be the ones to give us the go to proceed at T -5 [if everything is OK”]... so it’s looking our way ... we’re cautiously optimistic.”
10:45 a.m. update: Post reporter Brian Vastag, at the scene in Cape Canaveral, tweets: “NASA announcer George Diller just said weather is still a go”. Satellite and radar still indicate promising conditions - just scattered clouds, and no precipitation.
Overview: The last launch in NASA’s 30-year space flight program is set for 11:26 a.m. today. NASA’s final four astronauts have boarded the shuttle. However, the official Atlantic (STS-135) launch weather forecast assigns a 70 percent probability that weather will prohibit the launch.
Here’s an excerpt from the latest official forecast issued at 2 a.m.:
Scattered showers associated with a tropical wave are prevalent over the Kennedy Space Center area and the saturated atmosphere will continue to breed showers and thunderstorms today. Our primary concerns for launch are showers and thunderstorms within 20 nautical miles of the Shuttle Landing Facility, flight through precipitation, and cumulus clouds.
The National Weather Service forecast indicates a 70 percent chance of showers and thunderstorms through this afternoon.
At 10:30 a.m., however, weather radar did not show showers or thunderstorms in the vicinity of Cape Canaveral. And satellite imagery showed just scattered cumulus clouds in the vicinity. Based on the present conditions, I think odds of the launch going off are higher than 30 percent. In fact, I’d say they’re better than 50/50 at this point. Nonetheless, cloud cover could certainly increase with day time heating over the next hour, and showers could pop up.
As the National Weather Service in Melbourne, Fl said in its 4 a.m. discussion, the area is immersed in a “soupy airmass that will need little in the way of perturbation to generate precipitation.”
The update to this discussion released at 10:32 a.m. EDT conveyed a similar message:
HAVE SEEN SOME BREAKS IN CLOUD COVER THIS MORNING...BUT THESE WILL FILL IN AS DIURNAL HEATING AND SUBSEQUENT CONVECTION OCCUR LATE THIS MORNING/EARLY AFTERNOON AS A TROPICAL AIR MASS REMAINS IN PLACE