What would you do to the sky? Here is the pic before.
Darken it. If necessary, increase contrast to the sky area to find any detail you might have in the clouds.
There are usually many ways to accomplish any given task in PS. Here's the simplest way that comes to mind for darkening your sky -
Duplicate the background layer
Change its blend mode to Multiply
Reduce the opacity slider to taste
Mask off the bottom portion of the image. (Again many ways to mask. Easiest & quickest would be to add a white layer mask to the "Multipy" layer), then select a brush size with a soft edge, and paint black @ 100% over what you don't want darkened.)
This will get you well into the ball park. Fine adjustments to your own taste.