Since 1950, there have only been 19 F / EF4 tornadoes in the US during the last month of the year and only 2 F / EF5 tornadoes.
The last EF4 tornado to hit the US during the month of December was during the Christmas outbreak of December 2015.
The last EF5 tornado to hit the US during the month of December was in 1957.
An EF5 tornado is the strongest designation a tornado can receive. Exceptionally rare, these tornadoes can produce wind speeds in excess of 200 mph. The last EF5 tornado to hit the United States was Moore, Oklahoma, in May 2013. That was 3,125 days ago and is the longest streak on record.
This event was caused by a volatile atmospheric configuration that was poised to produce long-trajectory and violent tornadoes. Friday was unusually warm and record-setting temperatures that were more like spring than mid-December. This warmth, combined with the high humidity, provided enough fuel for the storms.
As the day progressed, the wind fields strengthened and helped create the dynamics, or “spin,” in the atmosphere necessary to produce tornadoes.
A cold front running through the region provided the trigger for the storms, which with all the ingredients in place created the conditions for a tornado outbreak.
Compounding the favorable atmospheric ingredients is the fact that the United States is currently in a La Niña pattern, historically increasing the frequency of tornadoes throughout the Mississippi Valley.
And climate change may also have played a role.
Research reveals that climate change may be causing the tornado alley to drift east, out of the traditional Great Plains tornado alley and into parts of the Mississippi Valley.
While meteorologists and climate scientists cannot yet say that the frequency of tornadoes is increasing globally Due to climate change, it can be said with relative certainty that the frequency of tornadoes and associated vulnerability is increasing in the Mississippi Valley and Midwest regions of the United States.
During a news conference Saturday night, President Joe Biden addressed the role that climate change may have played in the disaster. “Well all I know is that the intensity of the weather across the board has some impact as a result of global warming. The specific impact on these specific storms I cannot say at this point. I will be asking the EPA and others Take a look at that, “Biden said. “But the fact is, we all know that everything is more intense when the weather is warming up. Everything.”
Kentucky Governor Andy Beshear described the tornado as the most devastating to hit the state, estimating it could have killed at least 70 people or more than 100.
That will make this event not only one of the deadliest tornado events in Kentucky history, but also in US history, and potentially the deadliest December outbreak on record.
Nighttime tornadoes are more than twice as likely to cause deaths than their daytime counterparts. This is because tornadoes are harder to see at night and sleeping people often have no way of waking up when warnings are issued.