Tornadoes: looking into the eye of the storm

• December 2021 saw the highest number of tornadoes ever recorded for the month in the US
•  The tornado outbreak is estimated to have caused $4bn in insured losses
•  Even if property is not directly hit, tornado losses can be extensive, with roofs and windows blown out, and water damage to equipment
•  A possible link between climate change and tornadoes is still the subject of ongoing scientific research

In December 2021, a massive storm swept across the US, carrying heavy snow and rain into the West and northern Midwest of the country. In the South, which was enjoying near record-breaking heat via warm air from the Gulf of Mexico, the cold, dense air hit the warm air to create the perfect conditions for tornadoes.

Just outside Searcy, a small city in Arkansas (pop. 23,660), the supercell, a strong thunderstorm with rotating updrafts, began spawning a family of tornadoes with astounding staying power. One ripped through the rich surrounding farmlands, destroying barns, hurling cotton bales with fury and destroying power lines.

Another sliced through a nursing home in Monette and jumped the Mississippi River, where it plowed through the western edge of Tennessee. One EF4 tornado carved a 166-mile (267km) path of destruction.

Altogether, 66 tornadoes [1] were reported from December 10-11, causing widespread power outages, damage and 93 fatalities [2]. The devastating swarm of twisters marked the highest number of tornadoes recorded in December. This record stood only until December 15, when a larger outbreak produced around 100 tornadoes [3] across eight states.

The peak tornado season in the US is March to June, although tornadoes can occur at any time. A tornado struck New Orleans on 22 March this year (2022), killing at least one, after several swept through Texas and Oklahoma the day before.

Andrew Higgins, Senior Regional Technical & Expertise Manager for Allianz Risk Consulting at AGCS, remembers visiting Moore, Oklahoma, in 1999, six months after an EF5 tornado had passed. Tornado strengths are measured on the Enhanced Fujita (EF) Scale, which bases assessment on a scale of 0 to 5 estimated wind speeds and damage done. An EF5 tornado is the strongest, with winds over 200mph (322kmh) capable of lifting substantial houses and throwing them considerable distances.

“It was as if a mile-wide bulldozer had plowed through the landscape,” Higgins marvels. “There was nothing there to see except for downed trees and concrete slabs where buildings used to stand. A tornado can have such power it can wipe everything away down to the very foundations.”

Higgins has long been fascinated by the weather. As part of his duties today, Higgins develops technical procedures and policies used for risk assessing the facilities of Fortune 1000 companies. He also develops resources to evaluate the damage caused by windstorms, specifically hurricanes and tornadoes. 

“The December 2021 tornado outbreaks were unusual, but not unprecedented,” Higgins says. “And these tornadoes did not set records for intensity or duration on the ground. They did, tragically, set a record for December fatalities.”

The death toll of 90 (with three additional non-tornadic fatalities) surpassed the previous December record of 38 recorded during the Vicksburg, Mississippi, tornado of December 5, 1953. In some ways, it is surprising it has taken so long for the December record to fall. As Higgins notes, in 1950, the US had a population of 151 million. Today it is 330 million. Double the population means many more people living in areas where tornadoes are common.

It’s the sheer randomness of tornadoes that astounds Steven Kennedy, Regional Head of Property, Marine, Construction & Energy and Entertainment Claims, North America. Individually, they can be unpredictable to the point of caprice. As a young field adjustor, he once followed a tornado path through cornfields. The tornado had run straight and then suddenly veered off for a brick schoolhouse, which it smashed to pieces. 

Today, Kennedy is in charge of many of the areas where losses can potentially occur due to tornadoes. So what is his assessment of the December outbreak, which is estimated as causing $4bn in insured losses [4]? 

“Assessments are still ongoing, but we are involved in two large claims. One is a car manufacturing plant at around €150mn,” Kennedy explains, of which AGCS only has a small exposure. 

Allianz has little residential book exposure to tornadoes in the United States. Most is on the commercial risk side. The company has shared losses on claims of up to $400mn on direct tornado hits in the past. 

“Even if not directly hit, the damage can be extensive, as it was to the car manufacturing plant,” Kennedy explains. “Typically, the roof is damaged, and all windows blown out. That’s when the torrential rains enter, and you can have extensive water damage.” 

While the building can be quickly sealed, significant downtime can occur as the machinery dries and is tested to see what needs to be replaced. The costs can soon mount. 

All the famous cultural images of tornadoes — from Dorothy’s house being whisked away in The Wizard of Oz to the storm chasers in the surprise hit Twister (1996) – are set in the US. The reason is that tornadoes are mainly an American phenomenon.

“Every year, the United States gets about four times as many tornadoes as Europe,” says Hannes Roemer, Expert Cat Risk Analyst at AGCS in Munich, Germany. “In a typical year, Europe experiences 250-300 tornadoes [5]. In comparison, the United States experiences around 1,200. [6]” 

The reason is the Great Plains, the broad expanse of flatlands stretching east of the Rocky Mountains and west of the Mississippi River. This vast interior of grasslands and prairie – including the famed Tornado Alley – is an ideal breeding ground for tornadoes. There, warm, humid air from the Gulf of Mexico meets cold, dry air from Canada and the Rocky Mountains.

The dry air acts as a convection cap that prevents warm air from rising. The pressure builds until a cold front moves in and weakens the cap. Then the warm, humid air can burst out, billowing upwards and swelling into 50,000-foot-tall thunderstorms in minutes. Some storms begin rotating through most of their depth and generate tornadoes. 

No other place on earth has the intense conditions of warm, moist air on the equatorial side and a wide, high range of mountains running north to south on the west side. This favors the mixing of different-temperature air masses, whereas in Europe, air convergence is hindered by the Alps running west to east.

But tornadoes do occur elsewhere. Roemer notes that in Europe, most tornadoes are EF0, EF1 or EF2 (max wind speed 135mph/217kmh), while in the US, there are multiple EF4 and EF5 tornadoes every year. But there are exceptions.

“Only last year, a tornado with wind speeds of up to 260mph/418kmh in the Czech Republic killed at least five people and injured more than 200. The UK on average reports 30 tornadoes a year [7] and Germany 20 to 60 [8],” says Roemer. The most-deadly tornado on record occurred in Bangladesh in 1989, when 1,300 people were killed, 12,000 injured and 80,000 left homeless.

The record-warm December helped fuel the fourth-warmest year [9] for the US in 127 years of records. The temperature averaged 2.5F degrees above normal and fits into a long-term trend toward rising temperatures. All six of the warmest years on record in the US have occurred since 2012, says the US National Oceanic and Atmospheric Administration (NOAA).

Yet, scientists have low confidence in detecting a link between tornado activity and climate change [10], primarily because of the short length of high-quality data records. However, some scientists say warmer winter temperatures will create conditions favorable to the formation of severe thunderstorms and tornadoes, but such effects are not yet detectable.

NOAA noted the two December tornado outbreaks helped make 2021 the third costliest year of disasters [11] on records. The $145bn price tag, of which some $85bn [12] was insured, includes exceptional heat and drought in the western states, wildfires, a cold snap in Texas, four tropical storms and hurricanes, and nine severe thunderstorm/tornado events. The only costlier years were 2005, when Hurricane Katrina struck, and 2017, when hurricanes Harvey, Irma and Maria made landfall.