A major tornado outbreak affected the Midwestern and Southern United States from April 19–22, 2011, with 110 tornadoes being spawned across six days. From April 19–22, a storm system moved through from the Great Plains to the eastern U.S.. Thunderstorms began in the late afternoon and early evening with large hail and several tornadoes. Significant damage was reported near Bowling Green, Missouri and Girard, Illinois as a result of tornadoes, the latter of which was rated EF3. Another large tornado was reported near Octavia, Oklahoma before the supercells merged into a very large squall line. Overnight, the squall line tracked eastward with widespread wind damage and many embedded tornadoes across several states, a few as strong as EF2, but most were brief and weak. In the early hours of April 20, 2011, a tornado tore through a neighborhood in Oregon, Ohio, leaving some significant damage but no injuries. Also, three tornadoes struck New Albany, Indiana, and Jeffersonville, Indiana. Both are cities just north of Louisville, Kentucky.
Severe weather once again developed across parts of the Midwest on April 22. The hardest-hit area was parts of the St. Louis, Missouri metropolitan area. A destructive tornado tracked across the region with severe damage in several communities including houses destroyed in communities such as Bridgeton, Ferguson, Florissant, Hazelwood, Maryland Heights and New Melle. Lambert-St. Louis International Airport was hard hit with severe damage to numerous facilities there and injuries reported. Windows were blown out of the terminals there and airplanes were flipped in the field. Concourse C was the hardest hit, taking nearly a year to reopen; it reopened on April 2, 2012. The tornado was given a rating of EF4 based on finding of flattened houses in Bridgeton, one of them was fully leveled. Following assessments by the local National Weather Service, it was determined that a single tornado tracked for around through parts of Missouri and Illinois, reaching a maximum width of . Elsewhere, there were several reported tornadoes, including an EF2 tornado which tracked through Henderson, Webster and Union Counties in Kentucky.
Throughout this outbreak, other tornadoes also caused damage in Illinois, Ohio, Texas, Oklahoma, and other parts of Missouri during the period. No fatalities were reported in this multi-day outbreak. Just a few days after this outbreak, the largest tornado outbreak on record would occur, the 2011 Super Outbreak.
Meteorological synopsis
April 19–20 A severe weather event developed across the Midwest and southern Great Plains on April 19 as a dynamic low pressure system tracked across the area. Thunderstorms began in the late afternoon and early evening with large hail and several tornadoes. Significant damage was reported near Bowling Green, Missouri and Girard, Illinois as a result of an EF3 tornado. The individual storm cells later merged into a very large squall line. Overnight, the squall line tracked eastward with widespread wind damage and many embedded tornadoes across several states. A few tornadoes were as strong as EF2, but most were brief and weak.
April 22 On April 21, 8:00 PM CDT (01:00 UTC), the Storm Prediction Center issued two slight risk areas of severe thunderstorm activity across one region in west-central Texas to southwest Oklahoma, and another over the latter's northeastern corner, eastern Kansas, west-central Missouri and northwestern Arkansas for the following day. A large area of cyclonic flow interacted with two short-wave trough over the Pacific Northwest. Strong perturbation traveled from eastern Washington and Oregon towards Idaho. A leading, southern trough was forecasted to move eastward across the central Rocky Mountains, eastern Wyoming and the Nebraska Panhandle.
The following day on April 22, 1:00 AM CDT (06:00 UTC) the Storm Prediction Center (SPC) issued a widespread slight risk area spanning from central Texas to western Ohio, alongside a large 2% tornado risk for most of Missouri, Illinois, Indiana and northwestern Kentucky, as one of the two short-wave troughs was forecasted to weaken as it entered Wyoming from the northeast. Meanwhile the leading trough was expected to become even further perturbated, evolving into a 500-millibar low pressure area over northwestern South Dakota by 1:00 PM CDT (18:00 UTC) and accelerate to the east-northeast. Lee cyclogenesis over southeastern Colorado was forecasted to lift northeastwards along a strengthening front extending from southern Kansas to western Illinois, evolving into a triple point cyclone for the occluded surface low associated with the upper trough over South Dakota. At the same time, a cold front was forecasted to sweep eastwards across Missouri, Illinois to Ohio, with it later stalling over northwest Texas to southeast Oklahoma as a secondary, and weaker low developed. Advection and mixing was expected to force the dry line move to the east across west-central Texas and southern Oklahoma by day. The cold front was forecasted to overtake the dry line in south-central Oklahoma towards the surface low, where the triple point should be set up soon. As a result, multiple rounds of thunderstorms were expected to affect portions of this area to the Ohio River Valley, with 1000–3000 J/kg of CAPE from southern Missouri to the Indiana/Ohio state border area.
Severe weather once again developed across parts of the Midwest on April 22. The St. Louis metropolitan area was hit hardest by the storm system. An EF4 tornado tracked across the region. Severe effects occurred in several communities, including houses and other buildings destroyed in Bridgeton, Ferguson, Florissant, Hazelwood and Maryland Heights, Missouri, but also in Granite City, Illinois. Another tornado nearby struck areas near New Melle, Missouri. The EF4 tornado caused extensive damage to numerous facilities at St. Louis Lambert International Airport, with injuries reported; airplanes were damaged from the high winds and terminal windows blew out. American Airlines claimed four of their jets were damaged, two significantly. The airport was closed for days after the tornado. The EF4 rating was based on finding of a leveled house in Bridgeton. Following assessments by the local National Weather Service, it was determined that a single tornado tracked for through parts of Missouri and Illinois. It reached a maximum width of . Elsewhere, there were several reported tornadoes, including an EF2 which tracked through Henderson, Webster, and Union counties.
Confirmed tornadoes
Girard, Illinois
This intense and damaging tornado first touched down in the northeastern portions of Macoupin County at 5:58 p.m. CDT (22:58 UTC) on April 19, on Emerson Airline Road around to the west of Girard. Along this road, several homes suffered extensive damage as the tornado began to track northeastward. As it crossed Henry Road just to the north of the Henry Road/Emerson Airline Road intersection, it demolished several barns and struck three homes, with one being destroyed and another suffering significant damage, with debris trapping the homeowners in the basement until first responders arrived. Around this time, the tornado inflicted minor injuries to two individuals who were heading to the basement. The tornado then began to turn more eastward, destroying more outbuildings and striking several farm homes along Neff Road, with one being destroyed.
The tornado then approached Pleasant Hill Road around north of Girard, where a brick home suffered extensive damage with all nearby outbuildings being destroyed. The tornado continued to the east, destroying a farm and killing several cows before turning to the southeast. The tornado then crossed Prose Road around half a mile south of the intersection connecting Prose and Substation Roads, where a brick home had most exterior walls collapsed while interior walls remained standing. This home was given an EF3 rating, with wind speeds estimated at . The tornado turned and began to track southeast, inflicting moderate roof damage to a home along the Kimes Road/Adams Road intersection. The tornado then struck a farmstead along Adams Road, inflicting minor damage before lifting at 6:05 p.m. CDT (23:05 UTC).
The tornado had a very curved path as it went north around Girard, with a total length of and reached a maximum width of . Along its path, the tornado injured two people and killed numerous cattle.
Maryland Heights–Bridgeton–Ferguson, Missouri/Granite City, Illinois
During the evening hours of Good Friday, April 22, a supercell dropped a powerful tornado in the northwestern suburbs of the St. Louis, Missouri metro, at 7:59 p.m. CDT (00:59 UTC). The tornado touched down north of Creve Coeur Lake, in the northern parts of Maryland Heights at around EF1 intensity. After moving east and crossing the Missouri Eastern Railroad tracks, the storm intensified to EF2 strength, damaging poles along a wide swath before it slammed into its first neighborhood.
The tornado then became intense as it persisted eastwards, now at EF3 intensity as along Jeannette Mary Drive, one house had most of its walls collapsed, though some interior ones were left standing. EF2 damage occurred throughout suburban areas within Maryland Heights, located west of Interstate 270. Crossing over the freeway, the tornado maintained significant status, as it immediately tore the roof off one home along Charleston Drive before weakening down to EF1 strength. At the same time, path jogged a little northeastward, before the tornado returned on its easterly course. The storm then restrengthened back to EF2 status along Parkwood Lane, with a residence that had its garage collapsed and roof ripped away.
Now crossing over into Bridgeton and paralleling Old St. Charles Road, the tornado weakened slightly again and causing EF1 damage, before abruptly intensifying as it approached the three-way junction connecting Old St. Charles Road with Harmann Estates Drive. Encroaching on the T-junction, the storm gained intensity as it first caused high-end EF2 damage to a house, with winds now at at this spot prior to the tornado abruptly becoming intense as it moved a house down east. At this neighboring residence, the tornado with mid-range EF3 winds of only left a few walls standing. Thereafter, the tornado became violent as it inflicted EF4 damage to a house just to next door. Winds of winds collapsed all walls on this particular home, and EF3 tree debarking occurred north of the property. The tornado then weakened down to EF3 strength after crossing Harmann Estates Drive.
Along Beaverton Drive, a neighborhood was impacted at high-end EF3 status. The tornado afterwards paralleled Interstate 70 whilst remaining intense. Some buildings in a business district along the freeway were heavily damaged or destroyed, before weakening down to EF2 strength. Remaining strong, the tornado then skirted northern St. Ann before it struck St. Louis Lambert International Airport with surprise, despite earlier warnings. Parts of Terminal 1 were heavily impacted, with EF2 damage inflicted here. East of the airport, the tornado impacted neighborhoods within Berkeley, Ferguson and Bellefontaine Neighbors, leaving localized spots of EF2 damage behind. Crossing the Mississippi River into Illinois, the tornado weakened before entering northern portions of Granite City. For the last time, it caused EF2 damage to homes along Dawn Place before dissipating at 8:31 p.m. CDT (01:31 UTC).