According to Cerveny, megaflashes that extend hundreds of miles are rare, but it is not unusual for common lightning bolts to strike 10 or 15 miles out from its originating storm-

After further research, scientists were able to confirm that a single flash of lightning stretched horizontally across the sky for 515 miles from Texas to Missouri. This breaks the previous record for longest lightning flash of 477 miles that was produced by a complex of thunderstorms along the central Gulf Coast.