Extreme Temperature Diary-April 24, 2019/ Topic: Tornado Trends And Climate Change

Wednesday April 24th… Dear Diary. The main purpose of this ongoing post will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials.😉

Tornado Trends And Climate Change

It’s mid spring, so weather wise we are approaching the traditional height of severe season across the lower 48 states. When I was at the Weather Channel many of us debated how much climate change was beginning to have on systems that would produce severe storms. More northern latitude severe weather systems did catch our attention. Most of us blamed out of season, northern severe outbreaks on global warming trends, but could find no correlation with tornadoes. Now Climate Central has.

Personally, I spent a lot of time tracking surface record temperatures at TWC after 2000, so I left it to severe weather experts to spot any tornado trends. Through 2015 they could find none except for more severe outbreaks occurring farther north, so I congratulate Climate Central and associated researchers for their further findings. It makes sense that a warmer atmosphere would hold more moisture and energy for potentially stronger tornadoes.

Today’s main topic deals with tornado trends and climate change within the U.S. Here are Climate Central’s quoted and reposted findings released today:


Largest Tornado Outbreaks Getting Larger

Largest Tornado Outbreaks Getting Larger

  • Published: April 24th, 2019

By Climate Central

After a relatively quiet 2018, this year’s tornado season is already making an impact. Through April 22, 266 tornadoes have occurred in the U.S. in 2019. Even though a warming climate provides more energy for the thunderstorms that spawn tornadoes, it’s still unclear how climate change is affecting wind shear — the necessary spin that generates tornadoes. How tornadoes react to a changing climate continues to be vigorously researched, and some trends are surfacing.

There has been a subtle but detectable increase in tornado risk over the past few decades. Let’s be clear, tornadoes are not going away in the Plains and Upper Midwest, but more have been recorded east of the Mississippi. While there are connections to climate variability modes like ENSO, these overall trends are consistent with an eastward shift in the drier climate zone of the western U.S. and with climate change projections indicating that severe storm environments will become more common in the eastern U.S.

The number of tornadoes in large tornado outbreaks is also on the rise. In one study defining an outbreak as having six or more tornadoes in a six-hour period, there are about five more EF1+ tornadoes in the largest outbreaks now than in the 1950s, and another study showed that the number of days with 30+ tornadoes has also been increasing. One possible reason for the increase is that the weather environments that produce severe storms are occurring more often.

In addition to the changing geography and number of tornadoes, there is a shift in the time of year they occur. On average, tornadoes are starting about a week earlierin the year in the tornado alley region from Nebraska to Texas, and summer tornadoes are declining nationwide. But in the colder months between November and February, tornado frequency has increased, especially in the Southeast. More troubling, nighttime tornadoes, which are more than twice as likely to cause fatalities, are more common during these colder months of the year. Given the complex, forested terrain and high density of mobile homes in the Southeast, this region is especially vulnerable to these overnight storms.

Methodology: Tornado outbreaks follow the definition set by Tippett et al (2016) of six or more tornadoes in six consecutive hours nationwide. Thanks to the Michael Tippett and Chiara Lepore for providing SPC tornado count data. Tornado climatology is based on Gensini and Brooks (2018). Special thanks to Harold Brooks and Victor Gensini for their guidance with this Climate Matters.

Now here is Climate Central’s chart indicating where tornadoes across the U.S. are getting more concentrated:


Shifting Tornado Zones


Here is more weather and climate news from Wednesday:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity. In most instances click on the pictures of each tweet to see each article.)

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Guy Walton- “The Climate Guy”

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