Editor's note: Weather conditions at KSC do not look very favorable right now. Forecasters predict only a 30% chance that weather conditions will permit a launch today at 3:26 pm EDT. Things look to be much the same on Monday as well (40% chance) - but they do look better on Tuesday, July 4th (60%) [see launch weather report]
Editor's note: The following image showing Ops Commit Criteria, was shown on one of the KSC video feeds at 11:00 am EDT. With all the red (no go) ratings under "observed comditions", It doesn't bode well for a launch today.
NASA's Launch Blog - Mission STS-121
"If we scrub today due to weather, mission managers will meet later to decide if they want to make a third consecutive launch attempt or stand down for one day and try again on Tuesday."