This next part is completely optional, I personally think the piece looks good with or without the shadow but for the sake of practicing techniques lets dive right in! Start with the wand tool (W) selected and right click on the Smokes layer. At the bottom will be the option to do color range selection. Click on it to bring up the tool menu.
Here we can see a preview of the selection in white as well as adjust the "fuzziness" (works like tolerance). When the mouse is outside the box it works as an eyedropper to change the selection, play around with it a bit to get a nice dynamic selection of the smoke. I personally like this method as it will give us a shadow with a more organic feel with different opacities rather than a large dark mass. Once you have something you like click OK and it will bring you to our next step.
With your selection make a new layer on top of everything else (Layer > New > Layer, or Ctrl+Shft+N on PC and Cmd+Shft+N on Mac). Going into Select > Transform Selection we can move our selection into place on the ground keeping into account perspective and distortion.
Once you have it in a nice spot on the ground plane (keep in mind where the light is coming from, although not entirely accurate in this case its always something to keep in mind) feather it out a bit, with the wand tool (W) active right click and go to feather to soften the edge.
Now on the new layer we created on top we're going to fill our selection with a low opacity black brush like on the bottom left. However this still looks really stiff, so go over it (on a new layer) with a black soft brush giving you results similar to those on the right, a nice dark shadow with some dynamic opacity.
Go ahead and group those layers together for proper organization.
Moving on with our details lets add some snowfall, now a lot of people will use custom brushes to do this but for the sake of saving time I prefer to use pre-made textures. For this piece I used textures by Andrei Oprinca from PSDBox (wonderful resources!). To use these its fairly simple, you just want to bring them in and set the blending mode to screen. This will get rid of the black background on the images we've brought in (non destructive) and leave only the nice little white dots. Placing these around the image (on top of everything else and in their own group as shown before) will give us a really nice snowfall effect. Make sure to mask out any visible hard edges as well as the little logo in the corner!
Next let's add a little atmosphere behind the arch due to the glow of the fire. This is as simple as going over the area with a very soft low opacity (think 10% or so) and using the soft light and overlay blending modes and alternating between the reds/yellows/and oranges. We don't want this to be overwhelming just a nice touch of oranges next to all the blues and grays.
Next little detail is the helicopter, use the stock photo provided and practice using a combination of pen tool, magic wand, and selective color. With the stock photo being on a bright blue background this is pretty straight forward. The rotors might give you some trouble but with the refine edge tool you might have better luck!