Amid record warm weather in the Upper Midwest — more typical of April than February — severe thunderstorms erupted Thursday. The storms spawned at least three tornadoes and multiple reports of large hail across Iowa, Illinois and Wisconsin. The most intense twister hit southern Wisconsin, becoming the state’s first February tornado on record.
Temperatures some 30 degrees above average broke numerous records and helped fuel the unusual episode. Scientists say such severe thunderstorm activity will probably become more common in the winter months as temperatures rise because of human-caused climate change.
In addition to the twister in Wisconsin, tornadoes were also reported in Marshall County and Putnam County in Illinois, where a semitruck was overturned. In Chicago, thunderstorms sparked a dramatic display of lightning.
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More severe weather, inducing the possibility of a few tornadoes, is expected over portions of the Deep South this weekend and the Southeast by early next week.
The Wisconsin tornado
The tornado appears to have been on the ground for a formidable distance in southern Wisconsin — perhaps 15 to 20 miles — on a southwest to northeast path about 20 to 30 miles south of Madison, the state capital.
“We do have reports of damage in Albany, northeast toward Evansville and all the way northeast of Edgerton,” Taylor Patterson, a meteorologist at the National Weather Service in Milwaukee, said in an interview. “Reports were a lot of tree damage, snapped power poles. There was damage to multiple outbuildings, and then we heard of a lot of homes that were missing their roofs.”
The Weather Service assigned the tornado a “high end EF2” rating on the 0- to 5-scale for intensity Friday.
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The tornado was strikingly well-defined, with a funnel fully condensed to the surface, indicative of a relatively dry atmosphere and high cloud-bases.
New photos tonight. These are from Leah and Jade in Evansville, WI. Incredible photos of a possible tornado. The National Weather Service will be out surveying damage on Friday, so we will officially know more at that time. pic.twitter.com/ZhQ09jh8CC
— Tom Wachs (@Tom_Wachs) February 9, 2024How the tornado formed
The setup for the tornado began with an area of low pressure system over Minnesota on Thursday. That low inhaled air from all sides. From the south, it drew a filament of mild air northward with a hint of moisture. From the north, a surge of cold, dry and dense air crashed southeast. The air masses met along a cold front.
Moisture was expected to be a limiting factor and there almost wasn’t enough of it to support tornado activity.
Tornadoes usually happen when dew points, a measure of humidity, are in the 60s and 70s but can occasionally occur at somewhat lower levels. On Thursday, they managed to sneak into the 50s during the evening hours as a small pulse of moisture arrived from the south along a warm front. A dew point of 54 degrees was logged at the Monroe Municipal Airport shortly before the tornado touched down.
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A few other ingredients came together to support the tornado development:
Share this articleShare- Spin concentrated along the warm front: Warm fronts tend to be replete with low-level helicity, or twist. When a storm rides along a warm front, it gobbles up that twist and tilts it into the vertical, bolstering the risk of a tornado. That appears to have been the case Thursday.
- Storms merged: Multiple storms converged shortly before the tornado touched down, increasing available spin.
The National Weather Service issued five tornado warnings as the storms swept across southern Wisconsin, the most on record during February.
How climate change may have increased the tornado potential
Tornadoes and rotating supercell thunderstorms require two things: storm fuel (referred to by meteorologists as convective available potential energy or CAPE) and wind shear. Wind shear is a change of wind speed and/or direction with height that promotes spin in the atmosphere. There was exceptional wind shear, but the amount of fuel available to the storms from moisture and warm air was marginal at best.
That said, the amount of moisture and warm air was considerably greater than typical for the time of year — and this seems to becoming increasingly common in winter storm environments because of climate change.
Numerous warm weather records were set across the Upper Midwest on Thursday, including in Wisconsin, where some records were exceeded by as much as 10 degrees. Eau Claire hit 59 degrees, surpassing a previous daily record of 49 degrees. Its average high on Feb. 8 is 26 degrees.
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In Monroe, near where the tornado touched down, the average high this time of year is 28.9 degrees, but the airport hit 58 degrees.
“We tied the climate record for Madison of 55 degrees from 1925, and we also set records in Milwaukee,” Patterson said.
As climate change continues to influence the weather, the extent to which unseasonably mild and/or humid air masses can waft north in the wintertime is growing markedly. That is allowing thunderstorms and tornadoes to spread into what once were the typically quieter months.
An outbreak of storms in December 2021 produced the first tornadoes on record in western and central Iowa and parts of Minnesota during that time of year.
A study published in January 2023 concluded that supercell thunderstorms that sometimes produce tornadoes are projected to “escalate outside of the traditional severe storm season,” including late winter, as the climate warms.
Jason Samenow contributed to this report.
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