1953 Waco tornado outbreak

A deadly series of at least 33 tornadoes hit at least 10 different U.S. states on May 9–11, 1953. Tornadoes appeared daily from Minnesota in the north to Texas in the south. The strongest and deadliest tornado was a powerful F5 tornado that struck Waco, Texas on May 11, causing 114 of the 144 deaths in the outbreak. Alongside the 1902 Goliad tornado, it was the deadliest tornado in Texas history and is the 11th deadliest tornado in U.S. history. The tornado's winds demolished more than 600 houses, 1,000 other structures, and over 2,000 vehicles. 597 injuries occurred, and many survivors had to wait more than 14 hours for rescue. The destruction dispelled a myth that the geography of the region spared Waco from tornadoes, and along with other deadly tornadoes in 1953, the Waco disaster was a catalyst for advances in understanding the link between tornadoes and radar-detected hook echoes. It also generated support for improved civil defense systems, the formation of weather radar networks, and improved communications between stakeholders such as meteorologists, local officials, and the public.

The Waco tornado was not the only deadly and damaging tornado in the outbreak sequence. On the same day as the Waco disaster, a high-end F4 tornado struck the Texas city of San Angelo, causing catastrophic damage, killing 13 people, and injuring more than 150. The tornado swept away numerous homes and damaged a school, but students inside escaped without serious injuries. On May 9, a long-tracked F3 tornado destroyed a large swath of Hebron, Nebraska and killed five people in the area. The following day, May 10, featured numerous, often long-tracked and intense tornado families across the states of Iowa, Minnesota, and Wisconsin. Two families on nearly parallel paths traveled more than 100 miles (160 km) each and killed a combined total of six people, mostly in Wisconsin. At least one of the tornado families reached F4 intensity in Wisconsin. Two other F4 tornadoes also struck Iowa. Additionally, a relatively moderate tornado of F2 intensity caused significant loss of life in a shack in Minnesota, killing six people. Although 33 tornadoes were officially registered from May 9–11, others likely occurred but either went undetected or were not officially documented.

After two days of intense tornado activity, May 11, 1953, produced a rich, unstable air mass that moved northward over Texas from the Gulf of Mexico. As of 9:30 a.m. CST (15:30 UTC), thunderstorm activity from the overnight hours persisted, generating residual outflow boundaries. Already, anomalously warm surface temperatures reached the mid-70s °F (mid-20s °C) as far north as a line stretching from Dallas to Austin. Dew points were correspondingly high as well, climbing into the lower 70s °F. (lower 20s °C) As a dry line crossed the warm sector in the afternoon, a layer of cool surface temperatures left by the outflow boundaries locally enhanced low-level wind shear, acting as a mechanism to enable supercell and tornado formation. Winds backed along the outflow boundaries, perhaps aiding the formation of large and violent tornadoes. Due to conducive conditions for severe weather, the U.S. Weather Bureau (later the National Weather Service) Weather Forecast Office in New Orleans issued a tornado alert covering sections of Central and West Texas.

This destructive, large and violent, and extremely long-tracked tornado family likely contained at least five distinct tornadoes, spawned by one supercell. The first tornado in the series, though officially unconfirmed, may have formed near Greene in Butler County, Iowa, causing significant destruction on a farmstead. Continuous damage resumed near Chester, severely affecting 11 farms south of the Minnesota–Iowa border, with two injuries in Iowa. The storm then crossed into southern Minnesota, killing one person in a destroyed barn near Wykoff. Near Chatfield, the tornado carried a schoolhouse from its foundation, causing its disintegration. The tornado then hit a few cars halfway between Dover and St. Charles, one of which was carried 100 feet (30 m), injuring four occupants and killing the fifth, a child.

In Minnesota, four other people sustained injuries while inside a barn, and three more injuries were in another automobile; in all, 17 injuries were confirmed in the state. Across Fillmore, Olmsted, and Winona counties in Minnesota, over 24 farms received widespread, often severe damage, including the destruction of most buildings in some cases. The tornado downed many power lines and utility poles as well, and there was widespread loss of livestock. Entering Whitewater State Park, the tornado splintered "hundreds" of trees, and buildings in the park were badly damaged. After destroying a steel bridge near Crystal Spring, the tornado apparently dissipated into straight-line winds, though Grazulis suggested that tornado damage may have continued to Cochrane, Wisconsin.

Reports indicated that the storm crossed the Mississippi River into Wisconsin, where tornado activity definitely resumed northeast of Cochrane and ended near Brownville. As in Minnesota, damage was discontinuous, implying that two or more tornadoes were involved. Between Cochrane and Brownsvulle, the tornado hit roughly 100 farms, at least 20 of which lost buildings, and produced high-end F3 damage to some homes. "Hundreds" of dead livestock littered the landscape. Beyond Brownsville, the tornado(es) likely weakened and reformed into two, perhaps three, others, starting with spotty damage near Gilman. A farmhouse was swept from its foundation, and fragments of the home were lofted for seven miles (11 km). The tornado was reportedly exceptionally large and violent while southeast of Catawba, shortly before dissipation. Five injuries occurred in Wisconsin, though the actual total may have been 12.

Maximum damage intensity was F3 in Iowa and Minnesota and F4 in Wisconsin. The swath of damage between St. Charles and Whitewater State Park, Minnesota, across Olmsted and Winona counties, may have been from a separate thunderstorm, as Grazulis does not count it as part of the same tornado family.

This was the second of two long-tracked tornado families in Wisconsin on May 10. It first formed on the outskirts of River Falls and tracked to the north-northeast. Here, the tornado demolished a summer house, which collapsed onto occupants, injuring four who had been picnicking but had sought safety during the storm. Initially, multiple tornadoes were likely present, as damage was discontinuous until the tornado(es) passed east of New Richmond. At that point, a continuous swath of significant damage began and continued to near Amery. The first fatality, an elderly female, occurred in St. Croix County when her home was leveled, injuring three other people inside. Farther on, in Polk County, two additional deaths took place: one from flying debris, another in a destroyed barn. In Burnett County, the tornado felled a tree, which hit a dairy building, causing a final death. Beyond Amery, scattered, poorly documented destruction occurred for the remainder of the path. A separate tornado likely formed near Minong and dissipated near Gordon, destroying cabins and other small residences. Six injuries occurred across Washburn and Douglas counties, one of which was severe. There were 11 injuries near Amery and 27 along the entire path. Reports from local staff of the American Red Cross indicated that the tornado family destroyed or damaged 113 homes and affected 215 other structures. Collapsing barns killed livestock inside, though the precise number was undetermined. Numerous trees were downed along the path, and utilities were disrupted. The tornado(es) mostly impacted sparsely populated areas. While officially rated F2, the tornado was assigned an F4 rating by Grazulis, based on damage to homes near Amery.