To be honest, I don't really recall the precise work flow I utilized to get this image.

My usual process is to shoot in RAW and initially use Adobe Camera Raw. In this image, I lowered the blacks and shadows sliders slightly, and moved the temperature slider a good bit towards the blue temp. Highlights were reduced via slider, and the exposure was reduced from the initial image, which was exposed for the sky and left a lot of the image underexposed initially.

In PS I adjusted the white balance, and masked out the foreground and reduced the exposure to essentially remove all foreground details and make it a kind of silhouette effect. I then used a bit of luminosity masking to get the differing tones of blue in the different areas.

Hope this helps, but mostly I just tweaked these parameters around until I got the effect I was looking for...