This video, taken from the cockpit of an Airbus 321, provides a terrific perspective on the electrification of clouds. As the aircraft flies through the rain in the cloud, there are multiple electrical discharges across the outside of the windshields. Airbus windshield are non-conductive (they don’t use an anti-static coating) and as aircraft the flies through the charged cloud the the airplane (the conductive bits) attain the same potential as the cloud. The non-conductive windshields will remain at a fixed potential until the metal frame around the windshield (which is at the aircraft potential) discharges to bring the windshield to the same potential. As the aircraft flies closer to the center of the storm, the electrification will increase and the windshield discharges will become more repetitive.
One of the fall-outs of using non-conductive windshields is that the windshield will hold a charge for a very long time. Any mechanic who tries to clean the windshield will wind up with a strong shock and will probably wake up on the tarmac.
See the video below: