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Portions of Lubbock, Texas, were struck by a powerful multiple-vortex tornado after nightfall on May 11, 1970, resulting in 26 fatalities and an estimated $250 million in damage (equivalent to $1.96 billion in 2023). It was in its time the costliest tornado in U.S. history, damaging nearly 9,000 homes and inflicting widespread damage to businesses, high-rise buildings, and public infrastructure. The tornado's damage was surveyed by meteorologist Ted Fujita in what researcher Thomas P. Grazulis described as "the most detailed mapping ever done, up to that time, of the path of a single tornado." Originally, the most severe damage was assigned an F6 rating on the Fujita scale, making it one of only two tornadoes to receive the rating. Later, it was downgraded to an F5 rating after Fujita declared F6 damage was "inconceivable". The extremity of the damage and the force required to displace heavy objects as much as was observed indicated that winds produced by vortices within the tornado may have reached as high as 290 mph (470 km/h). Although skies were clear, dry, and sunny in Lubbock during the afternoon of May 11, the westward push of a dry line brought moist air into West Texas, providing suitable conditions for thunderstorm development. After 6:30 p.m., thunderstorms were in progress over the Lubbock area. At least two tornadoes developed prior to the main F5 tornado, including one that tracked across parts of eastern Lubbock near U.S. 87. The primary F5 tornado touched down in southwestern Lubbock at 9:35 p.m. and over the next half-hour carved a 8.5-mile (13.7 km) path of devastation encompassing roughly a quarter of the city, with the twister lifting near the Lubbock Municipal Airport shortly after 10 p.m. The tornado varied in size, spanning 1.5 mi (2.4 km) across when it first touched down before narrowing to around 0.25 mi (0.40 km) by the time it lifted. Severe damage was wrought to high-rises and other buildings in downtown Lubbock, including the 20-story Great Plains Life Building. The tornado briefly moved west and weakened, causing light damage to the campus of Texas Tech University before reintensifying and resuming a northward path. The tornado's most destructive impacts were observed in the Guadalupe barrio, north of 4th Street, along Texas State Highway Loop 289, and near the Lubbock County Club. In those locales, some homes were completely leveled and many others were irreparably damaged. Around 119 aircraft were damaged at the Lubbock airport where the Lubbock office of the United States Weather Bureau was located. As of 2024, this remains the westernmost F5/EF5 tornado recorded in the United States. Synopsis Developing storms (before 8 p.m.) The Severe Local Storms Unit (SELS) within the National Severe Storms Forecast Center (NSSFC) of the United States Weather Bureau – tasked with issuing daily outlooks projecting possible severe weather over the U.S. – did not initially highlight the possibility of severe weather over West Texas when the agency issued its daily outlook at 4 a.m. early on May 11, 1970. Six hours later, the SELS amended the outlook to indicate that "isolated thunderstorms with large hail" were "expected in High Plains of West Texas east of Pecos late afternoon and early evening." The afternoon was warm and dry in Lubbock with the temperature rising above 90 °F (32 °C) and the dew point remaining at around 40 °F (4 °C). As the air mass over the region became increasingly unstable, the forecast agency later advised of the possibility that some of the isolated thunderstorms could become severe. However, the atmospheric conditions aloft were generally unsupportive of a tornado outbreak. The skies over Lubbock were initially clear on May 11, with the ambient moisture too low to support severe convective storms on its own. However, moist air from the Gulf of Mexico spread north-northwest into the area during the day, providing sufficient buoyancy for convective development. Cumulus clouds began to proliferate over the region by around 4 p.m. and towering cumulus clouds began to develop over West Texas, darkening the skies over Lubbock. The WSR-57 weather radar site in Amarillo, Texas, began detecting radar echoes south of Lubbock at 6:30 p.m. Lubbock radar later picked up on a thunderstorm with a diameter of approximately 10 mi (16 km) forming near Woodrow, Texas, 15 mi (24 km) south of the Lubbock Municipal Airport. Satellite imagery from the ATS-3 satellite showed that the storm emerged about 15–20 mi (24–32 km) behind the leading edge of the advancing mass of moist air originating from the Gulf. Although the westward retreat of this boundary – known as a dry line – would typically coincide with nightfall and a stabilizing of the atmosphere, it did not move far from Lubbock during the evening, maintaining a local area of converging winds and moist rising air supportive of thunderstorm growth. These conducive conditions were also bolstered by the approach of a shortwave trough in the mid-levels of the troposphere, serving as another contributor to rising air. By 7 p.m. the northern fringes of the storm were near the Lubbock city limits. A rawinsonde launched from Amarillo concurrently showed that the tropopause had risen by 7,000 ft (2,100 m) to 48,000 ft (15,000 m) over the preceding 12 hours. The Amarillo weather radar also suggested that the thunderstorm's cloud tops were rising to at least 46,000 ft (14,000 m). Ironically, at the time the storm was developing, the Lubbock Civil Defense was holding a meeting to discuss disaster preparation plans, highlighted by showing the documentary film Tornado! (1966). The Lubbock Tornado itself became the subject of another documentary, Twister, with a subtle emphasis on a bumper sticker: "Lucky Me! I Live in Lubbock!" With the storm approaching and threatening to become severe, Alan Johnson of the Weather Bureau called Bill Payne, the director of Lubbock Civil Defense, to provide notice of the inclement weather. The emergency operations center (EOC) at the basement of the Lubbock city hall was activated at 7:45 p.m. Following discussion between forecasters at the local Weather Bureau office in Lubbock (Lubbock WBO, located at the Lubbock airport) and the radar operator in Amarillo, a severe thunderstorm warning was issued by the Lubbock WBO for Crosby, Floyd, Lubbock, and Hale counties at 7:50 p.m. with an expiration time set to 9:00 p.m. This warning was disseminated via the Emergency Action Notification Signal and through local radio and television stations such as KFYO. KFYO continuously ran without commercials after this time until 7:30 a.m. on May 14. Despite the increasingly conducive atmospheric conditions for the formation of severe thunderstorms, the NSSFC did not issue a severe thunderstorm watch or tornado watch for the region before storms developed. The Environmental Science Services Administration (ESSA) wrote in a service assessment of the weather event that the lack of s.... 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