Make lightening in Photoshop in just 3 and one half easy steps…
Start with the gradient tool set with default foreground to background and a medium gradient transition.
Add FILTER/RENDER/DIFFERENCE CLOUDS, use CTRL+I to alternate black to white.
Add a LEVELS adjustment CTL+L, and slide the black indicator almost all the way to the white indicator.
Now duplicate this layer CTRL+J, and set the blend mode to SCREEN. Rotate the new layer as you like.
(Figure 3 1/2)
Happy storm watching!