Concept
In this tutorial I will be showing you how to paint a rainy day scene without having to paint any weather effects, but rather the feeling will be conveyed purely based around colour, mood, and some reflections on the street. I took the photograph on the right myself, a long time ago. It is a good idea to always shoot your own reference material, because that way you don't have to worry about any copyright issues, especially if you want to sell your painting. When you are taking your reference, be sure not to use the flash. Using the flash will destroy any kind of lighting scheme you wanted and will also wash out the subject. Now that I have my reference I can get started...
The Block- In
(Fig01) For the most part of this tutorial I will just be using two different brushes for this painting; a round brush and a rectangular brush. When I am painting from reference material I open the reference and place it next to my canvas. This way I can always look over at the reference while I am painting. I start out by painting in the colour of the sky, and then block in the main silhouettes of the buildings in a dark colour, but not pure black. Right now I am using the natural, rectangular brush. I like using this brush because it is very versatile in the fact that you can get soft shapes as well as hard edges. You can also rotate the brush to get brush strokes in different directions. After I have all the main shapes in place I need to put in the base colour of the buildings (Fig02 - 03).

Fig. 01
Using the same brush I paint the buildings in the background with less pressure, as opposed to the buildings in the foreground. Usually things further away are softer, and things closer are sharper. Even when I know a building isn't going to be dark in colour, I will still block in the silhouette as a dark colour because that way I can get some of the dark colour to show through (Fig04). This will give the surface some more texture and depth otherwise it will look too flat. I continue to work all around the canvas and try not to focus on any one particular element (Fig05). This will allow me to get a greater feel for the image as a whole and not to worry about spending too much time on something, only to have it be out of place or in the wrong perspective.
Adding The Detail
One of the really cool elements in painting a cityscape is the lights (Fig06 - 07). The red tail lights of the cars act as a directional element that lead the viewer's eye throughout the piece. Adding lights will also give your illustration a livelier feel to it, almost as if it were alive itself. The brush I used to simulate rain droplets on the rear window of the car is a type of speckled brush (Fig08) (I also use this brush a lot when I am painting facial hair on men).

Fig. 08
The red tail lights look OK right now, but I really wanted them to feel like they were glowing. An easy way to do this is the use the "colour dodge” setting on the brush (Fig09). Do not use the actual Dodge tool because this will desaturate and wash out your painting, but instead use the Brush tool, and from the drop down menu select "colour dodge”. Using this setting will preserve colour in your painting and will make it glow. I usually pick a darker colour than what I want, because otherwise you will risk over-exposing your image. In order for this to work you will need to use this brush on a layer that has your entire illustration on one layer. If you are working in layers just hit the Ctrl + A hot keys to select the entire canvas, and then again hit Ctrl + Shift + C to copy all layers. Now just hit Ctrl + V to paste the illustration into a new layer. Now you can use the colour dodge brush on this layer. The other brush that I used a lot in this illustration was just a Photoshop, default, round brush, with the Opacity set to Pressure (Fig10 - 12).

Fig. 09

Fig. 12