The rocket is ready. The Dragon spacecraft is ready for its supply run to the International Space Station. But Mother Nature may not be ready for the launch of a Falcon 9 booster on Wednesday evening from Florida.

An unseasonably strong front has pushed into Florida, providing lift for atmospheric moisture and allowing for the development of widespread showers and thunderstorms. As a result, the official forecast for the 6:24pm ET (22:24 UTC) launch time—it is an instantaneous launch window, so the rocket must go at this moment—calls for just a 30 percent chance of “go” conditions. SpaceX will hope to get lucky and hit a gap in the storms this evening.

There is a back-up launch date on Thursday at 6:01pm ET (22:01 UTC), but unfortunately the weather appears to be about the same. If the rocket cannot get off the pad Thursday, the launch will likely slip into early August due to docking and undocking schedules of other visiting vehicles at the International Space Station.