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Here’s how rare that massive tornado in Kentucky actually was

Destiny Cartledge holds Desiray Cartledge, 3, in front of the rubble of a home ravaged by a tornado in Dawson Springs, Ky., on Dec. 12. (Austin Anthony for The Washington Post)

In the 70 years from 1950 and 2019, there were nearly 64,000 tornadoes recorded in the United States, according to National Oceanic and Atmospheric Administration (NOAA) data. Of that total, there was precisely one, a tornado that hit in 1952, that generally shared an unusual set of circumstances with the one that touched down over the weekend: It hit Kentucky in December and was measured at at least an F3 in intensity. It’s an unusual combination and, this time, a deadly one.

It’s not unexpected that there should be tornado activity in western Kentucky. We tend to think of tornadoes as being largely a function of the Plains states, open expanses where massive storms can form. But the region from the Appalachian Mountains to the Rockies has seen thousands of recorded tornadoes. The tornado that struck over the weekend that traveled from Arkansas into Kentucky is at the eastern edge of that range, but still within it.

Most of those tornadoes, though, didn’t occur in December. Spring is tornado season nationally, with twisters typically appearing farther north as temperatures warm each month. The NOAA data show tornadoes in each month, but far fewer in the autumn and winter, mostly touching down in warmer-weather states.

If we isolate just the storms in December in Kentucky over that period, the rarity becomes obvious. Again, this is 70 years of data, with only that tornado from 1952 measuring at least an F3.

The damage from that storm was not as severe as last weekend. Originating west of Louisville and then crossing into southern Indiana, it injured three people — including a kid hit by a pane of glass — but killed none. This weekend’s tornadoes left at least 64 people dead.

The NOAA’s data show a marked increase in the number of tornadoes in recent decades relative to previous years. From 1950 to 1989, an average of about 700 tornadoes were recorded each year, killing an average of 94 people. From 1990 to 2019, there were an average of 1,200 a year, an increase in part due to improved technology but also due to inconsistencies in how data were collected and tornadoes reported. Technology, like better forecasting and warning tools, has also helped lower the number of deaths; on average, 68 people died in tornadoes during the 1990 to 2019 period.

Again, though, notice the rarity of those December events. As The Washington Post’s team reported this weekend:

“It is unusual to have a severe storm outbreak of this intensity in December, when the warm, unstable air required to fuel intense storms is typically limited. But the record warmth swelling over the eastern third of the country created a storm environment more characteristic of March or April than December.”

The natural question, then, is the role that might have been played by global warming. Conservative media outlets were quick to insist that no such link can be drawn, but scientists don’t agree. A map published by Axios shows that the number of days with favorable tornado weather increased across much of the lower Mississippi River region from 1979 to 2020, including the area where this weekend’s storm originated.

Climate change models predict exceptional weather events. This weekend, Kentucky saw just such an event, a tornado so unusual that there are few historic comparisons.

* The historic Fujita scale for tornado intensity has been updated so that an F3 is not precisely comparable to a 3 on the Enhanced Fujita (EF) scale, but as a measure of relative strength, the comparison is still useful.

clarification

This article was updated with more information about the historic comparability of tornado counts.

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