Complex sentence: In total, 348 people were killed as a result of the outbreak, which includes 324 tornado-related deaths across six states and an additional 24 fatalities caused by other thunderstorm-related events such as straight-line winds, hail, flash flooding or lightning.
Split into simpler sentences: In total, 348 people were killed as a result of the outbreak, which includes 324 tornado-related deaths across six states. In addition, 24 fatalities were not caused by tornadoes, but were confirmed to be as a result of other thunderstorm-related events such as straight-line winds, hail, flash flooding or lightning.