1925 Tri-State tornado
In the midday and afternoon hours of Wednesday, March 18, 1925, the deadliest tornado in United States history and second-deadliest worldwide moved through Eastern Missouri, Southern Illinois and Southern Indiana, killing 695 people and injuring 2,027 more in what is sometimes known as the Tri-State tornado. The tornado touched down as part of a larger severe weather outbreak that hit the United States on the same day, and produced catastrophic damage across numerous villages and towns across all three states. Despite not being officially rated, it is widely accepted to have been equivalent to an F5 on the Fujita scale.
The tornado touched down in Shannon County, Missouri, moving to the northeast. The tornado immediately began to produce heavy damage to structures before directly impacting Annapolis, destroying ninety percent of the town and killing two people. The tornado then moved through Bollinger County, where it would hit two schools and injured several children who were taking shelter. Deep ground scouring was observed as the tornado moved past Sedgewickville, and debris from the town was found almost away. It would hit several other small communities, including Brazeau and Frohna, before crossing state lines into Southern Illinois and directly impacting Gorham. Over half of the town's population was killed, and the town was devastated as the tornado moved by. To the northeast, it would hit the northern portions of Murphysboro, where over one hundred residents would die as the tornado barreled through the town at an estimated forward speed of.
Further east, the tornado crossed into Franklin County, narrowly missing the towns of Royalton and Zeigler, devastating rural areas before heading towards the large mining town of West Frankfort. The tornado struck the northwest side of town, where in a manner similar to what was seen at Murphysboro, a number of densely populated neighborhoods, businesses and mining operations fell victim to the tornado. At the Peabody Mine 18 in Caldwell, a large 80-foot coal tipple weighing several hundred tons was blown over and rolled by the tornado. The tornado proceeded to devastate additional rural areas across Hamilton and White counties, between the two counties claiming 45 lives and injuring 140, 20 of whom later died. The tornado then exited Illinois, crossing the Wabash River into Gibson County, Indiana. The town of Griffin was completely destroyed, and the large town of Princeton ravaged before the storm passed into Pike County, where it dissipated over three hours after touching down.
The tornado killed at least twenty farm owners in southeastern Illinois and southwestern Indiana, more than the combined total of the next four deadliest tornadoes in the history of the United States. The tornado killed a combined total of 695 people, the majority of which occurred in Illinois.
Meteorological synopsis
The extratropical cyclone that set the synoptic stage for the outbreak was centered over northwestern Montana at 7:00 a.m. CST on March 17. Meanwhile, a diffuse area of surface low pressure was centered near Denver, Colorado, in association with a lee trough. Occluded fronts extended from Hudson Bay southwestward into the northern Plains states and into the lee trough. The synoptic cyclone moved south-southeastward across the mountain states to eastern Colorado. A warm front stretched along the Gulf Coast, separating warm, moist air from cool, showery weather with areas of fog that extended from Texas to the Carolinas. A well-mixed early-season continental tropical air mass existed over West Texas and northern New Mexico. To the east of this hot, dry air, buoyant maritime tropical air was advecting from the Gulf of Mexico. Simultaneously, a mid- to upper-level shortwave trough likely approached the northwest coast of the U.S. and moved rapidly through the persistent ridge then digging southeastward across the Great Basin and central Rocky Mountains and emerging in the Plains over Colorado. This initiated a Colorado low cyclogenesis.File:The_Tornadoes_of_March_18,_1925.pdf|thumb|"The Tornadoes of March 18, 1925" by the United States Weather Bureau, published in Monthly Weather Review in June 1925
At 7:00 a.m. CST on March 18, the surface low-pressure area, at approximately 1,003 hPa, moved to far northeastern Oklahoma while the warm front shot north into the circulation where the front then extended eastward. A maritime Polar cold front draped southwestward across eastern Texas with a dry line forming directly to the south of the low. The open shortwave, likely somewhat negatively tilted, was continuing to approach from the northwest and an apparent outflow boundary moved just to the south of the warm front over northeastern Arkansas and northwestern Tennessee. Several weak pressure troughs were traversing the cool sector over the north-central U.S.. Surface temperatures in the warm sector near the dry line and warm front ranged from, and the dew point was, with higher values farther south and increasing over time as the deepening low-pressure area continued to pull up air from the Gulf of Mexico. This resulted in unstable air and lower cloud bases, or low LCL heights, which is favorable to tornadogenesis. From southeastern Kansas to Kentucky and Indiana, early morning showers and thunderstorms north of the low and warm front cooled and stabilized that air, retarding northward advancement of the front, and led to a sharp contrast in temperature from north to south. Such baroclinic zones are also associated with tornadic storms. Ahead of the surface dry line, which are uncommon as far east as the Mississippi River, an apparent "dry punch" of air aloft served to further increase instability. Concurrently, a capping inversion likely suppressed storms throughout the warm sector, leaving the Tri-State supercell undisturbed by nearby convection.
By 12:00 p.m. CST, the deepening surface low was centered over south-central Missouri, the shortwave axis was moving easterly and oriented over eastern Oklahoma, and the dry line was rapidly advancing eastward directly south of the low as the warm front, situated due east of the low, slowly shifted northward. Morning clouds cleared by midday across much of the Tri-State tornado's eventual path. A pronounced pressure trough extended northeast of the low and signaled its future track as a prefrontal trough formed southeast of the low ahead of the dry line. A bulge in the dry line may also have been forming slightly south of the low, and southerly to southeasterly surface winds were backing and increasing with time throughout the warm sector. The tri-state supercell formed in a highly favorable area just ahead of the triple point where the cold front, warm front, and dry line met. The supercell initiated very near the surface low and moved east-northeastward, faster than the low, such that the storm gradually deviated east of the low's track.
By 2:00 p.m. CST, the low was centered slightly south-southwest of St. Louis, Missouri, as the tri-state supercell neared the Mississippi River. Other storms in the warm sector, removed from the supercell, were initiating around 3:00 p.m. CST. Around 4:00 p.m. CST, the low's central pressure lowered to around 998 hPa, centered over south-central Illinois, as the supercell was moving into Indiana. This pressure is not particularly low compared to many other outbreak setups, but the pressure gradient was strong, which induced strong gradient winds and significant advection in the warm sector. A very strong low level jet was also in place just above the surface as winds veered with height, resulting in low-level curvature and long hodographs. Strong wind shear thus existed, with pronounced directional shear likely in the vicinity of the warm front, with winds at the 700 hPa height level west-southwesterly around and winds at the 500 hPa level about. Theoretical hodographs returned estimated storm relative environmental helicity values of 340 m2 s−2 in the vicinity of the tri-state supercell track. Strong thunderstorms were now scattered throughout the warm sector and a line of severe thunderstorms was occurring near the dry line. The supercell appeared to still be discrete and isolated, with a severe storm north of Cairo, Illinois, placed well to its south.
Tornado summary
Shannon County, Missouri
The tornado was first sighted as a highly visible and relatively small condensation funnel in the rugged forested hills of Moore Township, Shannon County, Missouri, at around 12:40 p.m. CST. The funnel was spotted by Helen Thompson as it moved north toward Ellington around five minutes later. The Scott Farm suffered damage in this area, and the tornado was sighted by at least one farmer as trees in the area were destroyed. Farmer Sam Flowers was the first fatality of the tornado, being killed around 1:00 p.m. CST when he was struck by a falling tree. The tornado continued to be spotted as it moved south of the Redford area, and timber damage was reported in the Upper Low Hollow. Shortly before crossing into Iron County, a man cutting timber saw the tornado near the Black River. After entering Iron County, the tornado continued moving northeast, where a roar was audible as it moved near the Joseph Brown Farm. Three minutes later, the tornado directly impacted the mining town of Annapolis. On the northern side was the Annapolis School, where the tornado shattered windows and damaged doors. Downtown Annapolis was severely damaged; however, most of the business buildings and homes north of 2nd Street were not demolished. Closer to the railroad, there was complete destruction, and several freight cars were blown away off the tracks. At least 100 people were injured in downtown Annapolis and four were killed before the tornado moved on. An estimated 90% of the town was damaged.Madison and Bollinger County, Missouri
One minute after moving over Annapolis, it hit the small mining village of Leadanna. Some 21 homes were completely swept away, and several dozen more were damaged or destroyed. The mining plant was seriously damaged, the crusher mill and power house were completely destroyed, and the offices and other structures at the plant, including the tipple tower were severely damaged, although the smoke stack was left intact. Up to 50 people were injured in town when the tornado struck a mine, and three were killed, with inflicted damage costs totaling an estimated $200,000. The tornado then began causing a lot of damage over rural woodland, with large swaths of trees flattened north of the Collins School. It then crossed into the sparsely populated areas of Madison County south of Fredericktown, where the tornado steadily began to grow larger. Damage was inflicted to the Thomas Mills Farm north of Jewett, before the tornado moved south of the Cherokee Pass. In this area it damaged a home to the point where it was "torn from its foundation" and "tore down" several outbuildings on properties. A home on the Prichard Farm property was completely demolished, and a log house located east of the Castor River was destroyed, with several people suffering minor injuries. On the border of Madison County and Bollinger County, a property was "wrecked". After crossing into Bollinger County the tornado did significant damage to trees and rural farmhouses. On the Reva Henson Farm, the tornado sent a board flying through a hickory tree; everything on the property was destroyed. In this area, the tornado began producing ground scouring, with soil being torn up.The nearby C.M. Fadler Farm was also completely destroyed, and portions of the J.H. Johnson Farm were destroyed, with the top of his home being blown off and his timber suffering greatly with "greater portions stripped off". At 1:57 p.m., the Conrad School was directly hit by the tornado, with its concrete foundation being snapped and 18 children being injured. One child died the next day. Several others may have died later. The tornado caused pieces of tin to be entwined in tree branches on the Herman Bangert Farm; the pieces of tin remained there for at least 70 years after the tornado. As the tornado neared Lixville, a church and farm buildings were destroyed. A well-built house, possibly constructed with concrete, was partly destroyed by the tornado. On the property a piece of straw became lodged in solid concrete. To the north, the tornado began scouring the ground a second time from a farmhouse to the Garner School. The school itself was completely swept away by the tornado, with only a concrete foundation remaining. One person was killed and 29 others were injured at this location. Four more people were injured at a farmhouse to the northeast; the foundation was all that remained. On the Louis Clements Farm, significant ground scouring occurred, and one person was killed. Deep ground scouring was observed near the town of Sedgewickville as well, and the tornado carried sheets of iron as far as away. At around 2:00 p.m. the tornado crossed into Perry County, almost immediately injuring people and impaling livestock on snapped trees. One minute later a home was completely destroyed, with one death and another injury occurring.