Good New On 2018 Tornadoes, But There's An Ominous Study About Them

The last known EF5 tornado - the most powerful possible - in the
United States was this twister in Moore, Oklahoma back in 2013.
The storm killed 24 people. The U.S. has gone more than five
years without an EF5 tornado, which is a very unusually
long time between such disasters. 

It looks like we are about to conclude an incredibly benign year for United States tornadoes this year.

Despite an uptick in tornado activity in the Northeast during 2018, the nation as a whole saw relatively few tornadoes, and this will quite possibly become the year with the fewest tornado deaths on record.

On top of that, we're just concluding a rare year in which there were no EF4 or EF5 tornadoes, which are the strongest possible. These tornadoes have winds of 166 mph or more.

Tornadoes with an EF4 rating will level well-constructed houses and toss cars around. An EF5 tornado would take those leveled houses and fling them away to oblivion.  Cars would be tossed 100 yards or more, and even extremely sturdy high rise buildings would be twisted and destroyed.

Needless to say, EF4 and EF5 tornadoes, and their nearly as strong companions EF3s, cause the most tornado deaths. There weren't many EF3's this year either. At last count, the nation had ten EF3 tornadoes.

There was one EF4 tornado in North America in 2018: An EF4 killed one person in Manitoba, Canada this past August. 

Still, 2018's lack of strong United States tornadoes contributed to the thankfully low death toll.

So far this year, only ten people have died in the United States in tornadoes. That would be the lowest toll since 1875, when they started really keeping track of such things. The current record for least tornado deaths is 12 in 1912, followed by 15 back in 1986, says the Weather Channel.

The nation has been in a bit of a tornado drought, and an especially thankful tornado death drought since 2012. The average number of deaths per year is 69. In 2018 and 2017 combined, there were only 52 deaths between the two years, says data from The Weather Channel.

The last year we had an average or above average number of tornado deaths was 2012, when 69 people died in twisters.

Of course, the famous tornado year of 2011 was tragically much worse. That year, 552 United States residents died in tornadoes, which is a tie with 1936 for the second-worse tornado year. Some 700 people died in 1925, mostly in just one super tornado.

Never mind science, we are overdue for a bad tornado year, unfortunately. It's just a matter of chance. You'll eventually get a bad roll of the dice.

This happened in the United States with hurricanes. We went eleven years from 2005 to 2016 without a major hurricane hitting the mainland U.S. Major being Category 3 or higher. That was an unprecedented. We'd never gone that long without a major hurricane.

Then came 2017 with Harvey and Irma, the first time since 1851 two Category 4 hurricanes hit the U.S. mainland. (And then we had Maria trashing Puerto Rico and the Virgin Islands.).  This year brought hurricanes Florence and Michael.

Tornado activity can turn on a dime like this too. This aspect has little if anything to do with global warming. But it does beg the question: Does climate change influence tornadoes?

INCREASED TORNADO POWER?

A researcher, Dr. James Elsner of Florida State University, says one measure of overall tornado power in the United States is increasing.

The tornado drought in recent years notwithstanding, there hasn't really been a trend up or down in strong and violent tornadoes over the past several decades

Dr. Jeff Masters wrote about this recently in the Category 6 blog in Weather Underground:

"Tornadoes have been coming in bigger bunches with individual tornadoes being wider and staying on the grojnd longer, resulting in an increase in the destructive power of U.S. tornadoes averaging 5.5 percent per year since 1994."

I have to say I got a lot of pushback when I retweeted something on this a couple weeks ago. Meteorologist and business consultant Mike Smith correctly pointed to data that shows there seems to be a general trend toward fewer strong tornadoes (EF3 or higher) since 1954. However, Eisner's research didn't really say there are more tornadoes, just that there are more long-tracked, strong tornadoes during large outbreaks. 

The number of violent tornadoes has trended downward in recent
decades, but there are worrisome exceptions to this trend

So it's kind of how you parse the data.

Anyway, Masters in Category 6 goes on:  

"Eisner's study found that a given tornado is more likely to be strong or violent at night,  between 10 p.m - 4 a.m. and during the coldest months, between November and April. This counterintuitive result could be because there are fewer tornadoes overall at night and in winter, but tornadoes that do develop at these times are more likely to be in environments of strong wind shear, thus allowing their destructive power to be higher on average."

The above situation describes conditions in which there is a lot of instability in the air, which climate scientists say should increase in a warming world. However, another key ingredient for tornadoes is wind shear, which is wind that changes direction and speed with height. Climate scientists say wind shear should decrease overall with global warming.

The decreased wind shear would be most pronounced in the warmer months and less so during colder times of the year, so this fits well with Eisner's research, and what's been going on in the real world in recent years.

Four or five years do NOT make a trend, but there have been fewer tornadoes during the warmer months lately. Then again, there's 2011, so it's hard to draw firm conclusions.

It's possible climate change could make winter tornado outbreaks worse, but this is too preliminary for me to definitely go there. I want to see more research.

For now, I'll just go for a little of that dreaded wishcasting:  Let's hope that 2019 continues with the tornado drought.