To create a fog effect i followed one of Phlearns videos –
I made a new layer and then using his fog brush which is available on his website i painted fog in different sizes and colours picking from the lighter colours that were in the image, i did this on a couple of different layers so that i could play with the opacity. I then used a gaussian blur on the fog layers because it looked fake so with a bit of blur it softened the edges and made it look more realistic.
To change the overall colour i added a curves layer and played round with the red, blue & green channels until i was happy with it, i wanted something that was a bit moody and cinematic.
And to finish it off i downloaded a photo of a crow off google images and threw that in for added eeriness! 🙂
Below is the before and after –