@MatthewJensen has provided a very reasonable possible explanation. The OP has however indicated that the car left the parking spot before the rain. This prompts the consideration of an alternative mechanism:
In fact, if we constrain ourselves to inside-the-box thinking in a car-in-the-rain situation and approach this as a physics problem, these two ...
This solving process was a collaborative endeavor, starting here. It's been agreed that @msh210 will be making the next puzzle in the chain.
The first thing to notice:
Now, what can we do with this new picture?
So the answer must be...
THIS IS NOT AN ANSWER, BUT RATHER SOME NOTES ON THE MAKING OF THIS PUZZLE
@bobble provided the initial inspiration for combining the puzzle, and suggested I write some notes on its creation. Spoilers abound!
An almost-complete answer - just a handful of images still to identify 100% (4, 9, 12), but final answer found...
The answer to the puzzle is:
To reach this, we need to solve the eighteen Pictionary clues and then:
Clues resolve as follows (credit to solvers in discussions in the dedicated Chain Puzzle chat room):