Above is a type of lightning bolt that meteorologists call an "anvil crawler." They travel horizontally along the upper part of a thunderstorm(s).  Smithsonian  published an article recently about an anvil crawler that moved from Texas to Missouri -- a distance of more than 500 miles in about six seconds! This lightning event occurred in October, 2017.  If you wish to read the entire article it is here .  UPDATE:   The Wall Street Journal  had a (possibly paywalled) story about the lightning bolt today.