Darkened clouds by adding a second layer and overpainting with grey brush, then lowered the opacity.
step 2 of 5
Added some subtle (around 2.5%) monochrome noise to the picture to simulate distant rain. Applied 10 px motion blur and changed blend mode to 'multiply'.
step 3 of 5
Copied the second layer and stretched the top right portion to cover the entire layer. Rotated slightly.
step 4 of 5
Created a new layer and filled with black then added noise. Adjusted the brightness/contrast to maximise the white pixels, then resized a small portion from the top left to cover the layer. Applied motion blur, and changed opacity to 15% and blend mode to Color Dodge.
step 5 of 5
Created white lightning using the gradient/difference clouds/desaturate/screen effect (tutorial on this site), then coloured it blue. Added a white faded circle to simulate a burst of light from the impact point.