Anvil Crawlers are a type of lightning that can appear to crawl out of a cloud during a severe thunderstorm. In the development of a thunderstorm, an anvil cloud or towering cumulonimbus
cloud will form as a result of convective processes in the atmosphere. As the cloud grows taller and warm air rises, the charge potential in the top of the anvil could versus the bottom will be greater. Any time there is a difference in charge potential, there is a chance for lightning.
During the dissipation of a severe storm, multiple discharges of lightning that never appear to make it to the ground will appear to cling to the base of a cloud. Looking up at the cloud base, an anvil crawler will look like snakes of lightning swirling underneath the clouds.