May 28, 2016 Midwest Tornado Outbreak

Overview and Synopsis
On the morning of May 28, 2016, the Storm Prediction Center had issued a High Risk for much of the Midwest, including 45% tornado probabilities across portions of Illinois and Indiana, and 30% tornado probabilities extending into portions of Iowa, Wisconsin, and Missouri. A rapidly deepening low pressure system with a pressure of 994 millibars was located over portions of Central Iowa as of 15z. A 100 knot jet streak at the 500-millibar pressure level was located across portions of Oklahoma, and rapidly rounding the base of the trough, pushing its way northeast. An unusually well-defined dryline for so far east was draped southward from the low, as well as a sharp cold front approximately 100 miles behind it. A well-defined warm front was also draped from the low pressure center and into portions of northern Illinois and Indiana, with areas of convection lingering along it. However, by 17z, convection had cleared out, allowing for ample destabilization in the vicinity. By 20z, MLCAPE values of 2000-4000 j/kg had rapidly recovered in the warm sector and along surface boundaries. The surface low was now located over east central Iowa, with pressures down to 989 millibars, allowing for broad areas of surface winds backing to the southeast across eastern Iowa, northeast Missouri, northern and central Illinois, and northwestern Indiana. Combined with upper level winds veering to the WNW, intense speed shear, and surface boundaries, any updraft able to take advantage would violently rotate. By 21z, a moderate capping inversion began to erode away as the intense upper level winds moved into the vicinity. Intense supercells and a significant tornado outbreak ravaged portions of the Midwest, hitting Illinois particularly hard. Several supercellular waterspouts occurred on Lake Michigan as well, particularly off the Chicago shore, but these are not included in the tornado count since the National Weather Service does not count them as tornadoes. That being said, the outbreak had resulted in 237 tornadoes, 2,483 fatalities, over 10,000 injuries, and $25.9 billion in damage, making it by far the worst tornado outbreak so far in history.

"The Great Chicago Twister"
The tornadoes produced over eastern DuPage and central Cook County went down in history. This storm produced the new record widest tornado on record at 2.8 miles, beating the 2013 El Reno, OK tornado at 2.6 miles. The tornado was rated EF5 and caused apocalyptic destruction to the Chicago metro, taking a path straight through downtown. It was the tornado of nightmares, particularly to Chicago-area meteorologists who knew that the potential for such a catastrophic tornado event could happen one day. Meteorologist Tom Skilling, who covered the Plainfield F5 event in 1990 and has served as one of WGN-TV's meteorologists since the 1970s, stated that the damage, "outdid that of Plainfield's by leaps and bounds." He also stated that although he knew the potential for such an event was there, he, "didn't think it would be of this much of a catastrophic magnitude." The first Tornado Warning for this storm was out well in advance of the arrival of it, providing about 75 minutes of lead time. The supercell that spawned the Cook County tornadoes was a cyclic supercell that had already produced strong to violent tornadoes from its initial development near the Mississippi River, leading the National Weather Service office in Romeoville to issue these warnings so far out. The last tornado produced by this storm, an EF3, had lifted just before reaching the outer suburbs, near Sugar Grove. The storm then re-cycled and made a right turn as the mesocyclone churned away. This sealed in the fate of downtown Chicago, as its initial storm motion would've led it through the northern suburbs. At 8:34 PM CDT, the storm finally produced a tornado right over the Oak Brook Mall, doing EF2 damage to a Starbucks. It very rapidly intensified and grew, developing an EF2 satellite tornado to its south which damaged homes and businesses in Hinsdale and La Grange. Only minutes after its development, it entered the suburb of Westchester as a 2.5 mile wide EF5. Being that Westchester is less than 2 miles in length, the city was completely decimated. Portions of many other suburbs, including Broadview, Berwyn, Cicero, and Oak Park were also completely flattened. Amongst other satellites, an EF3 tornado developed just south of I-55 and paralleled for several miles. It did significant damage to portions of Midway airport as well as Archer Heights, Garfield Ridge, and Brighton Park. The tornado then reached its maximum width and intensity, at 2.8 miles wide with winds estimated up to potentially as high as 300+ mph in sub-vorticies, and entered the city of Chicago. Here, it did some of the most incredible natural distater-related damage known to mankind. The Willis Tower could not sustain the intensity of one mesovortex, and collapsed onto the city below. All other skyscrapers remained standing (besides those taken out by the fall of the Willis Tower), but sustained significant structural damage. The tornado did the last of its onshore damage at Navy Pier, wiping out most of the buildings and tossing the iconic Ferris wheel into Lake Michigan. Right as this happened, a small EF1 satellite developed and struck the Shedd Aquarium, where minor damage occurred.

All told, the tornado had killed 748 people, and injured 3,274, making it the deadliest tornado in US history. Many consider even this to be a miracle, as such destruction would have likely warranted death tolls in the thousands. Many believe that the early warnings from the National Weather Service allowed many in insufficient shelter to be able to find safe shelter with ample time to spare. Others were able to flee the path, although a large portion of fatalities were attributed to vehicles.

The Illinois Valley EF5
The same supercell that would later go on to produce the Cook/DuPage County tornadoes earlier had produced another EF5.

The supercell spawning this tornado had already been raging for two hours prior and produced strong tornadoes. As it approached the Illinois River, it was able to take advantage of the enhanced low level shear in the vicinity of an outflow boundary. The orientation of the boundary compared to storm motion was perfectly aligned; the storm followed it like train tracks. The twister quickly developed southwest of Camp Grove at 6:24 PM, doing EF1 damage to outbuildings and trees. It steadily gained intensity as it spared Camp Grove to the north, but slamming into Saratoga Center as 1.5 mile wide EF4, with winds estimated around 175 mph. It killed 5 here and injured 27. The tornado kept gaining intensity as it scraped the north side of the small town of Putnam, doing EF4 damage in town, but EF5 damage to a well constructed farm house just north of town. Immediately after, the tornado crossed the Illinois River, proving for the second time in 12 years that tornadoes can and do cross rivers in the area, after an F3 crossed the Illinois River in the same area just before killing 8 in Utica on April 20, 2004. Although no damage indicators struck by the tornado once it crossed go as high as EF5, entire forests were debarked, defoliated, and flattened. The pavement on Route 26 was stripped from the roadway and sod ripped from the ground, things only left behind by the strongest of tornadoes. EF3-EF4 damage was done to farms as the tornado indirectly hit. The tornado then moved into Mark and Granville, doing damage well beyond the EF5 threshold. All but the north side of Mark was flattened as well as all but the south side of Granville. A trailer park and farm were completely leveled just north of Granville, leaving only some slabs. Some of the mobile homes were thrown 5 miles away, as they were sent high enough to be caught thousands of feet into the storm before being dropped. At the same time, an EF0 satellite struck McNabb to the south, and an EF2 satellite developed and was quickly absorbed into the main circulation in the center of Granville. The death toll in Mark, Granville, and surrounding areas was 12. A major greenhouse was struck northeast of there, where glass shards could be found penetrating into wood miles away. The tornado now crossed the river again and struck the large towns of Peru and LaSalle head on. EF5 damage was also common here, with significant portions of the towns decimated. Death tolls here were 111. The tornado quickly weakened and shrank just after it left the towns, sparing small communities and rural farmsteads in the path. The total casualties were 128 fatalities and 478 injured.

O'Fallon, Missouri EF5 Tornado
The first tornado dropped by the supercell that spawned it, and it was a monster. This area, with its more veered surface winds, was less conducive for tornadogenesis that further northeast, but given excessive speed shear and still decent directional shear, a violent tornado was still able to take shape. The tornado developed very early in the outbreak, only minutes in as a matter of fact, at 4:43 PM. It was small and slow to organize for nearly half of its lifetime. Right when it crossed into more urban areas of the St. Louis suburbs, it quickly began to organize, strengthen, and widen. It grew to 2 miles wide as it plowed through Dardenne, doing high end EF4 damage. Thirty-four people were killed. An EF4 satellite tornado developed to its south, also doing severe damage and fortunately killing nobody. However, the tornado was absorbed into the EF5, possibly adding to its intensity. Hundreds of homes were already unrecognizable, but the worst of the damage had yet to be done. The main tornado very visibly became a violent multiple vortex tornado as it moved into the city limits of O'Fallon. Neighborhoods were leveled, although paths of vorticies were much more severely damaged than surrounding areas. EF3-EF4 damage was common outside of these vorticies, but swaths of EF5 damage were very clearly present in many areas. The death toll in O'Fallon was 219. The tornado stayed massive and violent as it ripped through the countryside on the other side of the suburbs, and killed 4 more as they were caught in their vehicles. The tornado eventually weakened and dissipated a few miles south of Kampville. The total death toll from the tornado was 257.

Madison-Sun Prarie, Wisconsin EF5
The supercell that spawned this tornado was well north of the warm front, but given moderate SBCAPE of around 2000 j/kg and the extreme helicity values that come with being north of the warm front, a monster EF5 was able to ravage the landscape. A low topped supercell developed southwest of Madison and soon after dropped a tornado at 5:35 PM. It did some EF2 damage to farms and outbuildings. Moving into Madison, it intensified into a mile wide EF4, flattening homes and doing significant damage to very sturdy structures. In the business district, one building was found to have sustained EF5 damage after closer inspection from engineers. A waterspout also developed on Lake Monona, but briefly moved over land before dying, confirming it as an EF0 tornado. The still very violent main tornado moved out of Madison and into rural, but still populated, areas. EF3-EF4 damage was still very prevalent here. The tornado moved into Sun Prairie at around 5:52 PM in its strongest phase. Much of Sun Prairie was completely devastated. Entire neighborhoods could justify EF5 damage rather than just single structures. The tornado was the strongest to hit the state of Wisconsin since at least the 1996 Oakfield tornado, although this one was likely stronger. The total death toll resulting from this tornado was counted at 182.

Champaign, IL to Lafayette, IN & Danville, IL Twin EF5s
The same long tracked supercell that produced the O'Fallon, MO EF5 and several other strong tornadoes later produced another EF5 as it ripped through east central Illinois. The first tornado was first reported on the ground at 7:01 PM between Monticello and Champaign. It did some EF3 damage to farmhouses soon after, and intensified as it moved into Champaign. Initially it did high-end EF4 damage, with winds estimated at around 190 mph. It completely destroyed especially northern portions of the Unviersity of Illinois campus as thousands of students sheltered there. Just before crossing I-74, it first showed signs of producing EF5 winds, as it swept a motel and several homes off their foundations. It also picked up and threw tens of cars caught on the interstate, as they couldn't get out of the way of the nearly 2 mile wide tornado in time. More EF5 damage was noted to neighborhoods northeast of the interstate, and several tombstones were ripped from the ground at Clements Cemetery just outside of city limits. Although the tornado was now tearing through primarily rural areas, the small towns of Royal and Collison, IL were wiped off the map. At the same time, another supercell was beginning to merge with the primary mesocyclone producing the primary EF5. This secondary mesocyclone also produced a tornado just north of Catlin, IL, and quickly intensified into another EF5 as it decimated portions of Danville. Winds of up to 210 mph swept multiple homes off their foundations, and several were killed. The tornado moved out of Danville, and now, instead of paralleling the primary tornado to the north, it turned toward it and merged with it over Bismarck, IL, right before crossing the border into Indiana. Here, mobile doppler radar acting as part of the ROTATE project measured wind speeds of 327 mph 100 feet above the ground, making it the most intense tornado known to mankind. Bismarck was completely swept off the map, with even some concrete slabs being ripped out of the ground. Next, the towns of West Lebanon and Attica, IN were scraped by the outer portions of the twister, producing EF4 damage. Independence, IN suffered a much worse fate, as EF5 damage was done in the center of the town. The tornado now moved into Lafayette as a 1.9 mile wide EF5 with winds still being measured to around 240 mph via mobile radar. Purdue University suffered an even worse fate than the University of Illinois in Champaign, featuring several buildings on campus being completely flattened. Numerous neighborhoods were also unrecognizable. The tornado started moving out of the city in a weakening phase, an EF4 moving out of town. It soon after began to shrink as it made a left turn with its occlusion. This didn't stop it from entering the towns of Bringhurst and Flora as a high-end EF3 and doing extensive damage. It made even more of a left turn as it moved northwest and readily dissipated east of Delphi, Indiana at 9:24 PM. All told, the tornadoes killed 185 and injured over 1,000.

Rochelle, IL EF5
A supercell with a history of destructive tornadoes in the Quad Cities area now produced another monster in an area hard hit by a high-end EF4 only a year beforehand, on April 9th, 2015. The tornado first descended a few miles southwest of Ashton, and intensified into an EF3 as it did extensive damage to the town. Flagg met a similar fate minutes later. Just as the tornado exited Flagg, however, it grew to a 1.5 mile wide EF5 as it moved into the center of Rochelle. Just outside of town, several train cars at a train station were thrown hundreds of yards from their original positions. The twister now moved into the heart of the town, leveling neighborhoods. Most notably, the Rochelle Community Hospital suffered incredible damage, reminiscent of the damage of St. John's Regional Medical Center after the May 22, 2011 Joplin, Missouri EF5 tornado. The tornado then moved out of town, doing EF4 to EF5 damage to farms in its path. Also notable was an EF2 satellite tornado to the tornado's south, which damaged homes and businesses in Creston. The main tornado then began to weaken and take a northward turn. The much smaller and weaker tornado still packed a punch in Kirkland, however, doing lots of EF2 damage and EF3 damage to a group of homes. The Rochelle EF5 killed 11 and injured 128.