Tornado outbreak of March 31 – April 1, 2023

A widespread, deadly, and historic tornado outbreak affected large portions of the Midwestern, Southern and Eastern United States on March 31 and April 1, 2023, the result of an extratropical cyclone that also produced blizzard conditions in the Upper Midwest. The Storm Prediction Center issued a rare high risk for severe weather in two areas of the Mississippi Valley on March 31, the first high risk issuance since March 25, 2021. Approximately 28 million people were placed under tornado watches, including multiple PDS tornado watches, from the evening of March 31 through the overnight hours into the morning of April 1. This included the Little Rock, St. Louis, Chicago, and Memphis metropolitan areas, all of which were hit by multiple rounds of severe squall lines and supercell thunderstorms that produced damaging winds, large hail, and tornadoes. EF3 tornadoes in Arkansas, Tennessee, and Illinois prompted the issuance of tornado emergencies and multiple mass casualty incidents were declared for some of the hardest hit areas. One of these tornadoes was a high-end EF3 tornado that passed through the northern Little Rock metro, causing extensive damage and dozens of injuries. The strongest tornado was a low-end EF4 tornado that swept away homes on the west side of Keota, Iowa. The Apollo Theatre in Belvidere, Illinois collapsed during a concert due to an EF1 tornado, injuring up to 40 concertgoers and killing one. Severe and tornadic weather also affected the Northeastern United States in the afternoon and evening of April 1, including a rare EF3 tornado that caused a death in Sussex County, Delaware. At certain points of the outbreak, over 20 simultaneous tornado warnings were active, with a total of 175 tornado warnings issued on March 31 with an additional 51 issued on April 1.
In all, 146 tornadoes touched down; 115 occurred on March 31 alone. The outbreak ranks third worldwide for producing the most tornadoes in a 24-hour period, with 136 tornadoes occurring between 19:00 UTC March 31 – 19:00 UTC April 1. That tally is surpassed only by the 1974 Super Outbreak with 148 in that 18-hour outbreak and the 2011 Super Outbreak with 219 in its busiest 24-hour period, although both of those outbreaks were far more prolific in the number of significant tornadoes produced. This was also the most tornadoes in an outbreak since the 2011 Super Outbreak. Tornadoes killed 26 people during the outbreak, along with one indirect tornado-related fatality. Six other weather-related fatalities took place: five from straight-line winds and one indirect fatality during cleanup. Additionally, over 218 injuries also occurred during the outbreak. Later in the year, tornado expert Thomas P. Grazulis published the outbreak intensity score as a way to rank outbreaks. The outbreak received 129 OIS points, ranking it as a historic tornado outbreak.

Meteorological synopsis

As another significant tornado outbreak was taking place across the Southern regions of the United States, the Storm Prediction Center had already highlighted a large 15% contour for severe weather across much of the area, where conditions were expected to become increasingly favorable for another severe weather event. By March 29, large sections of Iowa, Illinois, Missouri, southwestern Indiana, Arkansas, the western Tennessee Valley, and Kentucky were all given an enhanced risk for severe weather. In this region, a powerful mid to upper level trough was expected to eject and interact with an atmosphere containing elevated moisture given the moderate dew points across the area, and elevated low and high level jet streams. This made the environment favorable for the development of a strong, fast-moving squall line, and discrete supercell thunderstorms capable of damaging winds, large hail, and tornadoes.
By March 30, the Storm Prediction Center introduced a moderate risk for severe weather for two distinct regions in the northern and southern sections of the main risk area, where significant, long-tracked tornadoes were expected. In this outlook, the SPC discussed the presence of very high CAPE values reaching into the 1,000–1500 J/kg range, wind shear of more than 60 kt, and strong helicity of around 400 m²/s², which aided the sustainment of supercells. Two distinct areas were given a 15% hatched risk for significant tornadoes. The first stretched between southeastern Iowa and northwestern Illinois, and the second was in northeastern portions of Arkansas, the Missouri Bootheel, western Tennessee, small sections of southwestern Kentucky, and northwestern Mississippi.

March 31

An extratropical cyclone developed over Nebraska on the morning of March 31. As a result, meteorologists expected a storm mode of discrete supercells to develop. This, along with the presence of even stronger CAPE values and a more unstable environment across Illinois and eastern Missouri, led to the SPC "bridging" the two main moderate risk areas and giving a 15% hatched risk for significant tornadoes at their 1300 UTC outlook. The surrounding area, which extended into central portions of Kentucky and Tennessee, extreme southwestern Indiana, and northwestern Alabama, was given a 10% hatched risk for tornadoes. Additionally, a large 30% partially hatched contour for damaging wind gusts, and large hail were also added in this new outlook.
With increased confidence of favorable parameters for severe weather, the SPC upped the threat for strong tornadoes even further, introducing two tornado-driven high risk areas in their 16:30 UTC outlook; it was the first high risk issuance since March 25, 2021. In 2024, SPC forecaster and meteorologist Andrew Lyons stated, "we've been building up to this crescendo all week, knowing that pretty much all the parameters are there for something big and then one by one, each piece kind of fell in that morning." The first high risk area covered southeastern Iowa, northwestern Illinois, and far northeastern Missouri, while the second included eastern Arkansas, southwestern Tennessee, and northern Mississippi. These two distinct areas were given a 30% hatched risk for tornadoes, given the extremely favorable environment for the development and sustainment of discrete supercells with strong to violent tornado potential. The northern high-risk area was expected to see an arcing band of quasi-discrete supercells that would initially produce large hail before becoming tornadic with the possibility of producing several long-track strong to potentially violent tornadoes. Supercells would be more scattered, but longer tracked within the southern high-risk area with multiple rounds of tornadic storms capable of producing long-lived strong to violent tornadoes expected. The large area surrounding and connecting the two high risk areas maintained a moderate risk, with an accompanying 15% hatched risk for tornadoes, as supercells that could develop in this environment could similarly sustain and rotate, although storm coverage was expected to be somewhat lower, and the environment would not be as favorable. All throughout the main risk area, an elevated risk for damaging winds and large hail was also issued, with the supercells initially capable of producing very large hail and long-tracked tornadoes expected to transition into QLCS structures capable of producing very strong straight-line winds and additional tornadoes that evening. Soon after the upgrade into a high risk, the SPC introduced their first two particularly dangerous situation tornado watches, indicating a 90-95% chance for multiple tornadoes, and a 90% chance for multiple strong to violent tornadoes.
Not long after these watches were issued, isolated discrete supercells began to develop across the western part of the state of Arkansas. The first tornado, which was rated high-end EF3, to touch down in this area prompted a tornado emergency as it caused catastrophic damage and dozens of casualties in the western and northern part of the Little Rock metro. Later, another deadly long-tracked intense EF3 tornado moved directly through Wynne, destroying a large portion of the community. As that tornado moved in Tennessee and started to dissipate, the same storm produced another destructive EF3 tornado, which would become the largest of the outbreak with a width of over a mile, that struck the southern part of Covington, heavily damaging or destroying numerous structures, including homes and schools, along with more casualties. Farther to the north, discrete supercell development was much more widespread with several forming in northern Missouri, producing large to very large hail and gusty winds before quickly becoming tornadic as they moved northeastward into southeastern Iowa and western Illinois. One of the first tornadoes in this area was an intense high-end EF3 tornado that passed near Martinsburg, Iowa, severely damaging homes and outbuildings. As that tornado was dissipating, the same storm produced a violent low-end EF4 tornado, the strongest tornado of the outbreak, which passed near Keota, severely damaging and destroying several homes, including one home that was completely swept away. As the afternoon progressed, numerous tornadoes, including over a dozen EF2 tornadoes, touched down across this area from both discrete supercells and from an evolving squall line that moved into southern Wisconsin and northern Illinois. Farther to the south, additional supercells also began to form in Northeast Texas; these storms produced occasional large to very large hail and damaging wind gusts. East of there, another PDS tornado watch was issued for northwestern Alabama, northern Mississippi, and West and Middle Tennessee, in advance of isolated tornadic supercells that were moving eastward into the area and where more tornadic supercells were expected to develop.
After dark, despite the absence of daylight heating, strong wind shear continued to support the squall line over northern Illinois and southern Wisconsin. This led to widespread wind damage and several weak tornado touchdowns in the Chicago metropolitan area. This included a long-tracked EF1 tornado that struck the historic Apollo Theatre in Belvidere, Illinois, during a Morbid Angel and Crypta concert, causing a collapse of the venue's roof, killing one person and injuring at least 40 others. Additionally, an organizing cluster of severe storms with embedded supercells oriented from southwest to northeast continued to produce tornadoes, some of which were strong, as they moved northeastward through eastern Illinois into western Indiana. Another deadly high-end EF3 tornado spawned from a rogue supercell ahead of an advancing squall line in eastern Illinois and prompted yet another tornado emergency as it passed near Robinson, Illinois, before crossing into Indiana and striking the southern part of Sullivan, Indiana, causing damaging or destroying homes and mobile homes along its track. The squall line and lone supercell continued to produce mostly short-lived tornadoes as it moved through Indiana and into Ohio, although several of these tornadoes were strong to intense. This included another EF3 tornado that killed two people and injured two others on and east of McCormick's Creek State Park, and two more EF3 tornadoes that impacted Whiteland and areas east of Gas City respectively. Farther to the south, isolated supercells continued to move eastward, producing sporadic instances of severe weather. One intense supercell spawned two strong EF2 tornadoes that impacted Hardeman County and Bethel Springs, Tennessee, respectively. Later that evening, another isolated, intense supercell following along a similar track as the previous one produced a destructive, long-tracked EF3 tornado that also impacted Bethel Springs, as well as the northern part of Adamsville and Hookers Bend. This became the deadliest and longest-tracked tornado of the outbreak, killing nine people along a path of just over.