With the bulk of the lighting complete, it is now time to move on to the weather!
Weather
Fog is fairly simple to create and is quite quick to render, nothing needs to be setup in the scene in order to make this work. It's as simple as enabling it in the environment window. Firstly I hit the number key ‘8' to bring up the Environment Settings tab. I then scrolled down to the Atmosphere settings and clicked ‘Add'. This brings up another window with multiple choices of the type of effects you want to activate so I clicked ‘Fog' and pressed ‘OK'. This enables ‘Fog' to be added to the Atmosphere section on the Environment Settings tab. From this tab, I then selected ‘Fog' to enable the options to become visible.
Here are the settings I used for the Fog (Fig.20).

Fig.20
The fog provides a layered effect and silhouettes the buildings, helping to maintain the structures even in this dull weather condition.
Here is a render with the fog applied (Fig.21).
Street Lamp Lens Effects
The street lamp is the main focus so this needed to have more than just volume light applied to it. I used some Lens effects to give the impression of a light bulb glaring in the fog, casting shadows in the atmosphere. The final tweak was to make the light in the street lamp give off real characteristics of a light bulb. To get this effect I added Lens Effects to the MR-Omni light. This is done under the Atmosphere & effects tab of the light settings and adding a Lens effect from the add menu, the same way you would add volume lighting. Now that the Lens Effect has been activated on the light we can edit the settings in the Environment and effects window. Here you are presented with multiple options for effects, but for this scene I will only add ‘Glow' and ‘Ray'
Here are the settings I used for the Glow and Ray effect (Fig.22).

Fig.22