More Midwest Twisters: Why Is Oklahoma Tornado Vexed?
A second wave of tornadoes ripped through Oklahoma on Friday night.
Unlike earthquakes, which are often followed by aftershocks, the storms that birth tornadoes are independent of one another.
"By pure chance, we had two separate weather systems, both in very close locations and that ended up looking quite similar," said Christopher Karstens, a research scientist with National Oceanic and Atmospheric Administration's (NOAA) National Severe Storms Laboratory (NSSL) in Norman, Oklahoma.
In addition to spawning multiple tornadoes, Friday night's severe weather triggered a flash flood and hail the size of grapefruits. At least 5 people, including a woman and her baby, are reported killed. (Related: "A Tornado Chaser Talks About His Science and Craft.")
This week's tornadoes follow closely upon another devastating twister that touched down near the city of Moore,
