This is a full-on lightning storm. I started with bigger strings (E-strings) for the clouds, and progressed to smaller strings at the ends of each lightning bolt.
 
Here is the making-of video for this piece (and three others): https://youtu.be/vxQAm6uBxr8
 
It's a wooden canvas, stained white and set in table-top epoxy. Demensions are rougly 18"x11"