1. Use Gradient Fill tool to create a gradient.
2. Then go to Filter> Render> Difference Clouds and it will transform the gradient to this.
3. Image> Adjustments> Invert to swap the light and dark. You can see the lightning begin to appear.
4. Image> Adjustments> Levels. In the Levels control box you will see 3 sliders (black, grey, and white). Move the black slider to the right almost touching the white slider. You will see the clouds disappear and it will leave you with a lightning bolt.
5. To create several bolts just repeat the steps on a new layer. Gradient Fill.
6. Difference Clouds
7. Invert
8. Levels
9. To see both bolts, select the new layer in the Layers toolbar. In the dropdown menu that says 'Normal', select 'Screen'. This will allow the white from the lightning bolt to filter through to the next layer.
10. Then just move the new lightning bolt layer so it looks like it's branching off the first one you created.
11. You can create as many "branches" as you like. You can also adjust the color to give it a slight blue tint.
12. Finally, you can create a new layer and go to Filter> Render> Clouds. Then just merge all the lightning bolt layers together and bring it on top of the cloud layer.
