Complex sentence: It was part of an outbreak of thirty tornadoes that formed in eastern Iowa, northern Illinois and northern Indiana, in a short period of time but the Utica was the only tornado in that outbreak that caused fatalities.
Split into simpler sentences: It was part of an outbreak of thirty tornadoes that formed in eastern Iowa, northern Illinois, and northern Indiana in a short period of time. However, the Utica was the only tornado in that outbreak that caused fatalities.