At the part where Jo and Bill just got off the branch and are speeding away from the F5, the tanker truck is slammed down in front of them and explodes. If you look closely as the scene cuts from the explosion to their faces, you can see through the back window that there is nothing but sun shine and fields behind them, and the F5 is no where to be seen. That's pretty fast for an F5 to dissapate and come back, eh?