Jeff Masters Hurricane Blog

November tornado outbreak punctuates a quiet summer and fall » Yale Climate Connections

After the worst December for tornadoes in U.S. history, the summer and fall of 2022 have given the nation a break – for the most part. Stemming in part from the limited reach of this year’s landfalling tropical cyclones, widespread dry conditions in the central and eastern U.S. have been accompanied by dramatically fewer tornadoes than usual.

An exceptional mid-year stretch of nearly six months free of tornado deaths, starting on May 21, was broken on November 4, when two people died in a fierce regional outbreak that stretched from northeast Texas to western Arkansas.

The outbreak brought the year’s first two tornadoes confirmed at EF4 strength on the Enhanced Fujita Scale (see photo at top). “Violent” tornadoes are those rated EF4 or EF5, the top rating. Incidentally, the record-long stretch since the nation’s last confirmed F5/EF5 tornado – which occurred on May 20, 2013, in Moore, Oklahoma – will reach a decade in length next year.

July and August 2022 had just 96 confirmed U.S. tornadoes, the lowest total for those two months since 2013 (see Figure 1). The August total of just 32 twisters was the lowest for that month since 1967.

Figure 1. Official tornadoes reported in each July-August period in NOAA data extending back to 1950. Tornado reports increased from the 1950s to the 1990s with the advent of storm-spotting programs and the rapid growth in both storm chasing and high-quality imagery. (Image credit: Matthew Elliott, NOAA/NWS Storm Prediction Center)

Although data for September and October haven’t been finalized, they too were quiet tornado months. The preliminary totals of 19 and 45, respectively, are well below average. Once preliminary data are combed through – e.g., to eliminate duplicate reports – the final totals typically, but not always, edge a bit lower than before.

Another welcome statistic: relatively few tornado-related deaths. The U.S. toll of 20 fatalities through November 15 of this year could end up among the lowest on record if it holds steady. In contrast, 2021, 2020, and 2019 led to 103, 76, and 42 deaths, respectively.

A year earlier, 2018, was the least-deadly year on record for U.S. tornadoes, with a mere 10 fatalities.

As is now sadly typical, most of the nation’s tornado deaths this year have occurred in manufactured homes and vehicles. In fact, only three non-manufactured houses in the entire nation have experienced a tornado death this year. All were in Winterset, Iowa, which was ravaged by a long-track EF4 tornado on March 5.

Four of the victims in Winterset, all from the same family, were killed in a single house. Two other people died in houses just a few blocks away.

Figure 2. A mobile home destroyed by an EF2 tornado in Peason, Louisiana, on January 9, 2022. (Image credit: NOAA)

The hurricane factor (or the lack of it)

One reason for the scant number of tornadoes since mid-2022 is the limited influence of this year’s landfalling tropical cyclones.

During the peak months of hurricane season – roughly August to October – a notable share of the nation’s tornado activity typically comes from landfalling tropical storms and hurricanes. One study led by Roger Edwards (NOAA/NWS Storm Prediction Center, SPC) found that about 6% of all U.S. tornadoes from 1995 to 2009 were related to tropical cyclones. (SPC now has an experimental website that connects tornado reports with information from the HURDAT hurricane database.)

A single hurricane moving onshore can spawn more than 100 tornadoes, as was the case with both Ivan and Frances in 2004.

Two tropical cyclones have moved onshore into the contiguous United States in 2022, both in Florida. Those would be catastrophic Hurricane Ian, which produced a preliminary total of 12 twisters over southeast and east-central Florida on September 27 and 28, and less-cataclysmic but still-destructive Hurricane Nicole, associated with just one weak tornado in Virginia on November 11. In addition to these, Hurricane Fiona struck the U.S. territory of Puerto Rico on September 18, bringing more than $2 billion in flood damage and causing an estimated 25 deaths.

Two “close but no cigar” landfall candidates were Tropical Storm Alex ­– which passed over South Florida as a potential tropical cyclone, but got its name only after moving into the Atlantic – and anemic Tropical Storm Colin, which made landfall only in the sense of developing over land. Colin was designated a tropical storm while its circulation was already just inland near the coast of South Carolina, only to dissipate 24 hours later.

With this year’s U.S. tropical cyclone landfalls so limited in time and space, it’s no wonder there have been so few tornadoes since July.

Figure 3. Cumulative tornado counts for each year since 2005, including 2022 through November 16. This year’s cumulative total was running well above average in April, but fell below average by late June. (Image credit: NOAA/NWS/SPC)

Tornado seasons are becoming more variable

There wasn’t much talk about tranquility and tornadoes last winter and spring. The final month of 2021 was by far the deadliest and most prolific December for tornadoes in U.S. history. A total of 227 twisters was recorded, more than twice the old record of 99 from December 2002 and the highest on record for any month in meteorological winter (December, January, and February).

The two major events of December 2002 were a catastrophic nighttime-focused outbreak that took 89 lives on the night of December 10-11, centered on western Kentucky and Tennessee, and a swarm of 118 twisters along a record-setting storm system that ripped across the northern and central Plains on December 15.

Another sequence of tornado outbreaks arrived three months later, producing the greatest number of March tornadoes in U.S. history (234, beating the record of 194 twisters from March 2017).

Lurching from frenzied, record-setting tornado activity to near-record quietude, and vice versa, has become increasingly common in recent years.

As noted in a previous backgrounder on tornadoes and climate change at this site, there hasn’t been any long-term increase in the most violent U.S. tornadoes. Severe thunderstorms, and the tornadoes that cause them, are so naturally variable in the short term that it’s difficult to detect any climate-change-related increase or decrease. Moreover, there’s no particular reason to expect one. The conditions that lead to severe storms and tornadoes on a given day are localized and complex, affected by much more than climate-change signals such as long-term rises in surface temperature (see backgrounder for more details).

That said, changes do appear to be under way in when and where tornadoes form. Multiple studies have found an increased clustering, with highly active outbreaks and seasons interspersed with unusually quiet periods. This finding is consistent with the increased variability of the hydrologic cycle, which itself shapes when severe storms are most likely.

There’s also evidence for an eastward shift in tornado frequency, from the Southern Plains into the lower- and mid-Mississippi Valley (though the annual average tornado count remains higher in the Great Plains than further east).

Moreover, the monthly variability of EF1+ tornadoes has increased since the 1970s, with a growing occurrence of both record-busy and record-calm months, according to a 2014 study. And the most active and destructive tornado year in modern records, 2011, was followed by one of the quietest, 2012.

Events like the record-busy December 2021, which brought tornadoes as far north as Minnesota, also suggest a potential for more tornadoes at higher latitudes during cooler times of the year. It’ll take more time and research to see whether such possibilities might play out in a consistent way.

Above all, it’s important to keep in mind that tornadoes can develop anywhere, at any time of year – including Wisconsin in January – as long as the proper ingredients are in place.

Jeff Masters contributed to this post. Website visitors can comment on “Eye on the Storm” posts (see comments policy below). Sign up to receive notices of new postings here.

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