Although they are not common, tornadoes that occur in December are not uncommon. Meteorologists believe that Friday night's tornadoes were unusually strong and long-lasting, but they are likely to be placed in their own category. Experts said that one of the tornadoes -- if it was just one -- broke the nearly 100-year-old record of how long a tornado could stay on the ground in a path causing destruction.
Victor Gensini, Northern Illinois University meteorology professor, said "One word: amazing; unbelievable would be another." It was a late spring setup that took place in December.
Although warm weather was crucial in the tornado outbreak, meteorologists disagree on whether climate change is a contributing factor.
Scientists are still trying to understand how climate change affects tornadoes' frequency. However, they say that the atmospheric conditions that lead to tornadoes are becoming more severe in winter due to global warming. Tornado Alley is moving further east from Kansas-Oklahoma to states where Friday's victims were killed.
Here are some facts about Friday's tornado and climate change.
What CAUSES A TORNADO
Tornadoes, which are vertical air columns that spin around from thunderstorms, are created when they reach the ground. They are fast and destructive, and can destroy everything they come across.
Thunderstorms are caused by colder, denser air being pushed over warmer, humider air. Scientists call this atmospheric instability. When warm air rises, it creates an updraft. Wind shear is a condition where winds change in direction or speed at different altitudes. This causes an updraft to spin.
These wind changes produce the spin that is necessary to create a tornado. To produce strong tornadoes, you will need to make changes in the wind speed and direction.
Professor of meteorology at Pennsylvania State University, Paul Markowski said that tornado-producing supercell thunderstorms are possible when wind speeds vary significantly over the lower few thousand feet. "That's what happened yesterday."
Gensini stated that winters are characterized by a lot wind shear because of the large temperature and pressure differences between the Arctic and the Equator.
Gensini stated that there isn't usually enough instability to cause tornadoes in winter because it's less warm and humid. It was this time.
WHAT CONDITIONS CAUSE STORMS IN THIS SCALE
These are just a few of the factors that meteorologists will continue to analyze.
The warm, humid air that formed thunderstorms was brought by spring-like temperatures in the Midwest and South in December. La Nina, which brings warmer than average winter temperatures to the Southern U.S., is partly responsible for some of this. Scientists also predict that unusually warm winter weather will become more common as our planet warms.
"The worst-case scenario occurred. John Gordon, a National Weather Service meteorologist from Louisville, Kentucky, stated that warm air was in the cold season during the middle of the night.
Experts believe that tornadoes were not dissipated once the storm had formed. However, extremely strong wind shear appeared to have stopped them from dissipating after the storm had formed. When thunderstorm updrafts lose energy, tornadoes can die.
Gensini stated that while tornadoes usually lose energy in minutes, in this instance it took hours. He said that Friday's storm traveled more than 200 miles (322 km) on its own. The 1925 tornado that hit three states set the record at 219 miles (352 km). Gensini believes that this record will be broken once meteorologists have finished analyzing it.
A fast-moving storm is necessary to create a long path. Gensini stated that the storm averaged over 50 miles per hour (80 km) for most of its time. This is not because of the speed of winds but the overall storm movement.
Gensini stated, "You're referring to highway-speed storm motions."
WHAT IS CLIMATE CHANGE TO TORNADO EXTRABREAKS?
It's complicated. Scientists still struggle to determine if human-caused climate changes is making tornadoes more frequent or more intense. According to the NOAA National Severe Storms Laboratory, approximately 1,200 tornadoes are recorded in the United States each year. However, this number can fluctuate. There are more twisters than any other country.
It is difficult to attribute a particular storm such as Friday's to climate change. According to Harold Brooks, a scientist at the National Severe Storms Laboratory, only 10% of severe thunderstorms result in tornadoes. This makes it difficult to draw conclusions about climate change or the processes that lead up to them.
Scientists have noticed changes in the basic ingredients that make up a thunderstorm. However, this is changing as the planet heats. Gensini claims that extreme storms are becoming more common as we have warmer air masses during the cool season, which can support these kinds of severe weather outbreaks.
Brooks stated that the U.S. will likely see more tornadoes in winter as the national temperature rises above the long-term average. Brooks said that fewer events will occur in the summer.
Furtado of University of Oklahoma stated that tornado alley, which was a term used for the area where twisters struck the U.S.A., has moved eastward into the Mississippi River Valley. This shift is due to temperature, humidity and shear increases.
He stated, "Bottom Line: People in the Mississippi River Valley or Ohio River Valley are becoming more vulnerable to tornadic activities with time."
This story incorrectly states that the 1925 tornado only affected three states and not four.