Here is a whole field done this way – it took about 10 minutes. By the time I was to the front, I was using more noise, and setting distance to 6.
I added some trees in the back, again using the blur tool on top of some scribbles and noise, then drew some very rudimentary trees on top.
Finally, I quickly painted in a few random grass strokes towards the front, and here’s a finished field, suitable for a distant background, done in about 12 minutes.
Another idea: Rain
For this picture, I needed a rain effect. I also needed to do it quickly! On top of that, I didn’t want the rain to look terribly up-front, but just enough to give the idea it was there without taking over. Enter the Motion Blur filter! (Hooray!)
Start with the Brush took set to Dissolve (another much-overlooked feature) at about 5% opacity. Paint on a new layer above your background; I’ll show this on black so you can see it better:
