Complex sentence: During this week-long event, 152 tornadoes touched down (including one in Canada), more than half of them on May 3 and 4 when activity reached its peak over Oklahoma, Kansas, Nebraska, Texas, and Arkansas.
Split into simpler sentences: During this week-long event, 152 tornadoes touched down, including one in Canada. More than half of these touched down on May 3 and 4 when activity reached its peak over Oklahoma, Kansas, Nebraska, Texas, and Arkansas.