The calendar may say January, but — fueled by record-challenging warmth — the atmosphere is behaving like it’s March or April. A slew of tornadoes, as well as severe thunderstorms with damaging winds and hail, have ripped across parts of the South, Midwest and even California amid multiple rounds of dangerous weather so far this month. Another episode could strike the South on Wednesday just six days after tornadoes killed 10 people in Alabama and Georgia.
Midway through January, the National Weather Service has already received 124 preliminary reports of tornadoes. That number far outpaces the national average of 36 for the month, although a small number of reports are unconfirmed and may be duplicates.
Monday bore witness to a pair of tornadoes in an unlikely place: Iowa. The state hadn’t seen a January tornado since 1967, according to the National Weather Service, and these were the earliest recorded during the month. The twisters, which touched down near Cedar Rapids, may be the farthest northwest tornadoes ever observed during January.
It was only a little more than a year ago that central and western Iowa saw their first reported tornadoes during December amid another out-of-season event.
These events have all shared a common ingredient: abnormally warm temperatures. Human-caused climate change — and the expanding presence of warm, moist air over the southern and central United States during the dead of winter — are probably helping to fuel these violent storms.
Although studies have yet to definitely tie recent winter tornado outbreaks to global warming, the characteristics of recent severe storms “are consistent with climate projections, including studies that have specifically looked at future severe weather,” wrote Victor Gensini, a professor of meteorology and severe storms researcher at Northern Illinois University, in an email.
In other words, the recent onslaught of severe winter thunderstorms could well be a harbinger of what’s to come.
Another storm outbreak — boosted by warmth — expected Wednesday
The onset of the next severe weather event, fueled again by much warmer-than-normal temperatures, is less than 12 hours away as the storm that soaked California on Sunday and Monday enters the central states. On Wednesday morning, the storm was centered near the Oklahoma-Kansas border and was dumping snow in Denver and parts of Central Plains.
Ahead of the storm, a warm, humid air mass will waft north and spread across the Deep South, with predicted highs on Wednesday about 20 degrees above normal. A few locations in Mississippi could set records in the mid- to upper 70s — temperatures more typical of springtime.
In the zone coinciding with these toasty temperatures, the Weather Service’s Storm Prediction Center has outlined a level 2 out of 5 risk for severe weather. That risk zone encompasses much of the lower Mississippi Valley, including in Memphis; Shreveport, La.; and Little Rock.
Fueled by warm, unstable air, thunderstorms will grow vertically into an environment characterized by wind shear, or change of wind speed and/or direction with height. A pronounced dip in the jet stream will be sweeping overhead, causing thunderstorms that poke into it from below to rotate. That could make for some tornadoes.
The tornado risk may be limited somewhat by the structure of the thunderstorm complex that forms. It’s likely storms will align themselves along a cold front, clustering into a squall line that will propagate east with time. That should make for a broader risk of damaging straight-line winds, but a lesser tornado risk. That said, a few twisters could spin up.
A deadly January
January — one of the warmest on record to date — has already featured multiple swarms of serious storms across the South. On Jan. 2, thunderstorm complexes rolled through the south central United States, spawning tornadoes in Oklahoma, Louisiana, Arkansas, Tennessee and Kentucky. The next day, more than two-dozen reported tornadoes whirled through Mississippi, Alabama and Georgia. Simultaneously, a more localized batch of nine tornadoes touched down in Illinois. The storms progressed east on Jan. 4, even producing a rare January twister in southern Virginia.
On Jan. 10, an EF1 tornado, on the 0 to 5 scale for intensity, occurred at 4:10 a.m. in Calaveras County, Calif., south of Sacramento. Not only are tornadoes a rarity in California — tornado warnings are unusual. It proved the first time on record that the National Weather Service office in Sacramento issued an overnight tornado warning. An additional tornado, rated EF0, touched down in Sacramento County on Saturday.
The Weather Service logged 60 reports of tornadoes in seven states across the South during last Thursday’s deadly outbreak. Alabama was hardest hit. The most devastating twister tracked 76 miles over central and eastern Alabama, reaching a maximum width of 76 miles while killing seven people and injuring 16 in Autauga County. The twister, rated EF3, “obliterated” manufactured homes and hurled a pickup truck 120 yards, according to the Weather Service’s storm survey.
Role of climate change
Tornadoes need two things to form — instability, or fuel in the form of warm and humid air, and spin. The latter is ever-present during the winter because of a strong and proximate jet stream, but the former is tougher to come by — usually.
However, recent years have been a different story — there’s been no shortage of such fuel. On Dec. 10, 2021, an enormous EF4 tornado killed 58 people in Mayfield, Ky., stemming from a larger outbreak of tornadoes more characteristic of the volatile springtime. Five days later, a derecho, or violent windstorm, blasted through parts of the Plains and Cornbelt. Winds gusted well over 100 mph, and more than 70 tornadoes were confirmed. Record-setting warmth set the stage for both events.
The heightened severe storm activity observed during the past two winters has significant linkages to prevailing storm tracks associated with the ongoing La Niña event. La Niñas tend to feature storm systems, strengthened by a powerful jet stream, that sweep from the Rockies toward the Upper Midwest. Such storms customarily tap warm air from the Gulf of Mexico and draw it into the South. But human-caused climate change is giving this warmth a boost.
With the Iowa storms, for example, the Plains were about 15 to 25 degrees warmer than average. In the case of last week’s Deep South outbreak, water temperatures in the Gulf of Mexico — directly responsible for juicing up the lower atmosphere in Alabama — were 5 or 6 degrees above average.
In years past, tying tornadoes to climate change often meant making leaps. Nowadays, and particularly with cold-season setups, science is accumulating to support the linkage.
A study published this past summer in Geophysical Research Letters, co-authored by Gensini, projects increases in winter thunderstorm activity in both the South and Midwest. Moreover, a study published this month in the Bulletin of the American Meteorological Society, which Gensini also contributed to, finds that supercells — or rotating thunderstorms — will see “dramatic” increases during winter in future decades.
“These results suggest the potential for more significant tornadoes, hail, and extreme rainfall that, when combined with an increasingly vulnerable society, may produce disastrous consequences,” the study concludes.