No, it wasn't the weather after all. It wasn't even the dinged tiles from yesterday, or anything to do with falling debris on the orbiter.
But no, it wasn't something completely new either. It was a gremlin from the recent past, a malfunctioning fuel gauge that had showed up back in April, and never really got figured out, but the engineers convinced themselves it was ok. It wasn't. Can't fly with a busted fuel gauge, even if it is one of four redundant units. Safety demands it.
So the earliest they could fly, if they find it and fix it very fast, is Saturday. If it's harder, they might have to roll back to the Vehicle Assembly Building. In that case, they almost certainly can't meet the July launch window, and would have to defer until Sept. 9 at the earliest. We'll probably know by tomorrow sometime.