High Winds Tear Across Great Plains and Midwest

A potentially destructive storm system generated unusually powerful winds, dust clouds and possible tornadoes as it moved through parts of the central United States on Wednesday, causing scattered damage and forcing the temporary evacuation of the main air traffic control tower in Kansas City, Mo.

The storm system spun off severe thunderstorms in the Mississippi River Valley, just days after tornadoes whipped through at least six states — Arkansas, Illinois, Kentucky, Missouri, Mississippi and Tennessee — causing widespread destruction and killing at least 88 people.

The National Weather Service received reports of 19 tornadoes on Wednesday — all in Iowa and Nebraska. At least one tornado was reported in Plainview, Minn., according to the National Weather Service. There were no immediate reports of significant damage or injuries.

At 5:50 p.m., Kansas City International Airport officials announced that the Federal Aviation Administration staff had been temporarily evacuated from the airport’s air traffic control tower “for their safety.” They returned about 40 minutes later. A spokesman for the airport, Joe McBride, said in a text message that while staff members were away, they “did not work remotely, so we were at air traffic control zero.”

Videos posted on social media showed heavy rain pounding Overland Park in Kansas, a tornado whipping through Lincoln, Neb., and dust storms in Colorado and Kansas. Images circulating on social media showed damage to hangars and small planes at the Santa Fe Regional Airport in New Mexico. The storm system also spawned wildfires and winds up to 100 miles per hour in Kansas, according to the authorities there.

By Wednesday night more than 410,000 customers had lost power across Colorado, Kansas, Nebraska, Iowa, Illinois, Minnesota and Missouri, according to poweroutage.us.

Schools closed early in Iowa on Wednesday, where record high temperatures reached the lower 70s. On average, high temperatures in December throughout much of Iowa are in the 30s, according to the Weather Service.

Wind gusts of up to 90 m.p.h. swept through the state. The airport in Sioux City, Iowa, experienced a gust of wind reaching 82 m.p.h. at 4:24 p.m., according to the Weather Service in Sioux Falls.

As storms moved through South Dakota, the Weather Service office in Sioux Falls issued its first tornado warning on record for the month of December, a spokesman for the Weather Service said.

“The storm system is unprecedented,” said Andrew Ansorge, a meteorologist with the Weather Service in Des Moines. “We don’t have anything to compare it to.”

“Off the charts is the best way to say it,” he said.

By Wednesday afternoon, winds of up to 93 m.p.h. were reported as a line of storms moved through Lincoln, Neb., according to the Weather Service. Meteorologists for the Weather Service working in Omaha had to take shelter for a brief period during the storm.

In Kansas, high winds and blowing dust forced several highways to close, according to the state’s department of transportation. “If you don’t have to travel, don’t,” the department said.

A.J. Mumm, the emergency management director for Polk County, Iowa, which includes Des Moines, said in an interview that 98 of the state’s 99 counties were under high-wind warnings. School districts were warned on Tuesday to let students out early on Wednesday, and public employees were being sent home.

Transportation officials were shutting down bridges and warning drivers — especially those with “high profile” vehicles like buses, tractor-trailers and recreational vehicles — to stay off the roads, Mr. Mumm said.

Portions of western Iowa and southeastern South Dakota were bracing for winds with gusts of up to 65 m.p.h. until midnight local time, powerful enough to topple trees and power lines. Widespread loss of power was expected, Mr. Mumm and the Weather Service predicted.

“Its impacts will be felt north and south in a couple-hundred-mile swath,” he said.

Isabella Grullón Paz, Alyssa Lukpat and Azi Paybarah contributed reporting.

The same storm system generating tornadoes in the central United States also spawned high winds in Kansas that were the cause of dust storms and — by knocking over power lines — several wildfires, the authorities said.

Winds reaching as high as 100 miles per hour generated fires throughout the western and central parts of the state, said Jane Welch, a spokeswoman for the state’s Division of Emergency Management. At least one home was destroyed, she said, but no deaths or injuries were reported by Wednesday night.

Forecasters had said earlier that gusty winds, dry air and warm temperatures would create conditions ripe for “an extreme to potentially catastrophic grassland fire.”

Eric Metzger, a meteorologist at the National Weather Service in Wichita, said the biggest fire on satellite imagery is in Russell and Ellsworth Counties in central Kansas, where two fires had “merged together into one massive fire.”

“It’s probably about 40 miles long,” he said, adding that the fire was moving eastward.

He said that before Wednesday, Kansas had not had any rain for over a month. The state has seen fires in December, when the weather gets dry, but this felt different.

“I’ve lived out here for more than 20 years,” he added. “This is historic for us.”

He said the same storm system that generated rain and tornadoes could also whip up fires because the Gulf of Mexico had blocked moisture from moving north.

Ms. Welch said the winds were so strong on Wednesday night that it was too dangerous for emergency crews to fight the fires from the air. The smoke had already gotten so bad that it could be detected up north in Nebraska, the National Weather Service there said.

In addition to the fires, which prompted several evacuation orders, high winds have blown over eighteen-wheelers and dust storms have whipped through the state, hindering visibility, Ms. Welch said.

“It’s a little crazy in Kansas today,” she said.

A tornado watch was in effect through 8 p.m. Central time in parts of Kansas, Missouri, Nebraska and South Dakota. Parts of Minnesota, Wisconsin, Iowa and Illinois were under a tornado watch until 11 p.m. Central time.

The watches were a result of a storm system that formed in the Four Corners region, where Colorado, Utah, Arizona and New Mexico meet.

It was sweeping into the upper Great Lakes on Wednesday, bringing high winds that exceeded 70 miles per hour in some locations. In Kansas and Colorado, wind gusts could spike even higher, possibly to 90 miles per hour.

Strong winds and dense fog were forecast to hamper travel in Minnesota and northeast South Dakota through Thursday, while an onslaught of cold air could turn rain into snow, the Weather Service said.

The same dense fog and wind conditions were moving through Taylor County in north-central Wisconsin, the Weather Service said.

A powerful storm system moved through the Central United States on Wednesday, prompting a series of tornado watches and warnings, just days after a destructive series of tornadoes tore through at least six states.

The back-to-back weather events on Friday and Wednesday are unusual in December, with tornadoes typically occurring in the spring in the United States.

“The storm system is unprecedented,” said Andrew Ansorge, a meteorologist with the National Weather Service in Des Moines. “We don’t have anything to compare it to.”

As storms moved through South Dakota, the National Weather Service office in Sioux Falls issued its first tornado warning on record for the month of December, a spokesman for the Weather Service said.

A string of tornado warnings were also issued in Nebraska on Wednesday afternoon. Since 1950, Nebraska has recorded only two December tornadoes, which both occurred in 1975, according to the National Weather Service.

A tornado watch on Wednesday night extended into parts of Wisconsin, a state that has only recorded six tornadoes during the month of December since 1844, according to the Weather Service.

What prompted the unusual December weather events is unclear. The ingredients that give rise to tornadoes include warm, moist air at ground level; cool dry air higher up; and wind shear, which is the change in wind speed or direction. Each of these factors may be affected differently by climate change.

Friday’s tornadoes may have occurred because the wind shear was high (it tends to peak in the winter) and the weather was warmer than normal. This year, the region has experienced an uncharacteristically warm December, and temperatures in Arkansas and Kansas on Friday were in the 70s and 80s.

Parts of the Midwest also experienced daily record high temperatures on Wednesday. In Iowa, record high temperatures reached the lower 70s, nearly double the average high. On average, high temperatures in December throughout much of Iowa are in the 30s, according to the Weather Service.

Winston Choi-Schagrin contributed reporting.

Social media quickly became a place where people could share their experience of the powerful winds sweeping through the central United States.

One television reporter, Greg Payne of KCTV5 in Kansas City, was doing a live shot when heavy winds began ripping part of a roof off a building at the downtown airport. Bad weather also forced Federal Aviation Administration staff at the Kansas City International Airport to evacuate the air traffic control tower for about 40 minutes.

In Bellevue, Neb., “Several homes damaged tonight and large trees down everywhere!” a lieutenant in the local police department wrote on Twitter. “Heed storm warnings!”

Jeffrey Frame, a teaching associate professor in the department of Atmospheric Sciences at the University of Illinois, shared an image on Twitter of a giant plume of dust spreading from eastern Colorado and western Kansas all the way to eastern Nebraska.

The image is of a “midlatitude cyclone,” he said. “We see dozens of them from fall to winter to spring.” This one in particular, though, is “very intense.”

The pressure at the center is “very low” but it gets a lot higher toward the outside, Mr. Frame said. And it is that change in pressure “that creates these very strong winds, and it’s these very strong winds that have kicked up this dust and blown it several states away.”

In Colorado, large trees were uprooted and knocked over, with at least one landing on the back of a truck. In Jefferson, Iowa, there were “a couple buildings destroyed” by heavy winds, or possibly a tornado, according to a self-described storm photographer.

By the city of Pueblo, Colo., one person shared video of what was said to be a “massive dust storm” heading toward the city. Another dust storm creating “near-zero visibility” was recorded in Elkhart, Kan.

In Iowa, flashes of lightning lit up the sky in South Ames. Video of heavy winds with pounding rain were shared from Overland Park, Kan., to Lincoln, Neb.

President Biden flew to Kentucky on Wednesday to survey the damage wrought by a series of deadly tornadoes last weekend, reprising a role comforting disaster victims that has become a staple of his presidency and promising that the federal government would cover the full cost of emergency response efforts for the next month.

Even as a potentially destructive storm system bore down on the country’s midsection, Mr. Biden walked the previous storms’ paths of destruction in a pair of communities in the southeastern corner of the state, past entire blocks of buildings leveled by the high winds. He hugged survivors and promised that his administration would partner in relief efforts until residents and business owners could fully rebuild, describing the devastation as “almost beyond belief.”

“I intend to do whatever it takes,” Mr. Biden said in brief remarks from an intersection in battered Dawson Springs, Ky., “as long as it takes, to support your state, your local leaders, as you recover and rebuild — because you will recover and you will rebuild.”

The president said he had amended a disaster declaration for Kentucky to have the federal government cover the entire cost of debris removal and overtime for law enforcement and emergency personnel for the next 30 days. He said federal officials were helping to provide electricity, search-and-rescue assistance and shelters for victims, along with mental health services for those traumatized by the experience.

It was an all-too-familiar routine for Mr. Biden, who said on Wednesday that disasters related to extreme weather and climate change had inflicted $99 billion of damage on the United States this year. The president has made several similar trips to disaster areas since taking office in January. He has visited with victims of hurricanes and extreme storms on the Gulf Coast and in the New York area, and with victims of wildfires in the West.

The deadly tornadoes that pummeled six states on Friday, killing more than 80 people and leaving dozens missing, came at the end of a year of compounding extreme weather events, from heat waves and hurricanes to flooding and wildfires.

Scientists have been able to draw links between a warming planet and hurricanes, heat waves and droughts, attributing the likelihood that climate change played a role in individual isolated events. The same can’t be said for tornadoes yet.

“This is the hardest phenomenon to connect to climate change,” said Michael Tippett, an associate professor of applied physics and mathematics at Columbia University who studies extreme weather and climate.

Even as scientists are discovering trends around tornadoes and their behavior, it remains unclear the role that climate change plays. “For a lot of our questions about climate change and tornadoes, the answer is we don’t know,” said Harold Brooks, a senior research scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory. “We don’t see evidence for changes in average annual occurrence or intensity over the last 40 to 60 years.”

What causes a tornado?

Tornadoes form inside large rotating thunderstorms and the ingredients have to be just right. Tornadoes occur when there is a perfect mix of temperature, moisture profile and wind profile.

When the air is unstable, cold air is pushed over warmer humid air, creating an updraft as the warm air rises. When a wind’s speed or direction changes over a short distance, the air inside the clouds can start to spin. If the air column begins spinning vertically and rotates near the ground, it can intensify the friction on Earth’s surface, accelerating the air inward, forming a tornado.

How are they measured?

Like hurricanes and earthquakes, tornadoes are rated on a scale. The Enhanced Fujita, or EF, scale, runs from 0 to 5.

The tornado that traveled across Northeast Arkansas, Tennessee and western Kentucky over the weekend was estimated to be three-quarters of a mile wide with wind speeds that peaked between 158 and 206 miles per hour, giving it a EF rank of at least 3.

Because it’s challenging to measure the winds in a tornado directly, surveyors usually evaluate tornadoes by their level of damage to different structures.

For instance, they may look to see if the damage is limited to missing roof shingles or whether entire sections of roofs or walls are missing. Based on the level of damage, scientists then reverse-engineer the wind speeds and assign a tornado a rating on the scale.

Have tornadoes changed over the years?

Researchers say that in recent years tornadoes seem to be occurring in greater “clusters,” and that the region known as tornado alley in the Great Plains, where most tornadoes occur, appears to be shifting eastward. The overall number of tornadoes annually is holding steady around 1,200.

Tornadoes in the United States in December are unusual. They typically occur in the spring. Friday’s tornadoes may have occurred because the wind shear was high (it tends to peak in the winter) and the weather was warmer than normal. This year, the region has experienced an uncharacteristically warm December, and temperatures in Arkansas and Kansas on Friday were in the 70s and 80s.

Is climate change the cause?

The ingredients that give rise to tornadoes include warm, moist air at ground level; cool dry air higher up; and wind shear, which is the change in wind speed or direction. Each of these factors may be affected differently by climate change.

As the planet warms and the climate changes, “we don’t think they are all going to go in the same direction,” said Dr. Brooks of NOAA. For instance, overall temperature and humidity, which provide energy in the air, may rise with a warming climate, but wind shear may not.

“If there is not enough shear to make something rotate, it doesn’t matter how strong the energy is.” he said. “If there is all kind of wind shear, but you don’t have a storm, you won’t get a tornado, either.”

Although we know that climate change may be playing a role in making some storms more powerful, the complexity of tornadoes means that it is hard to extend that connection with certainty, especially for an individual event.

Scale is everything

A tornado’s relatively small size also makes it harder to model, the primary tool that scientists use when attributing extreme weather events to climate change. “We are working at such small scales that the model you would use to do the attribution studies just can’t capture the phenomenon,” Dr. Brooks said.