At 10 am on 11 May 1970, the SELS (Severe Local Storms unit) issued an outlook that stated that isolated thunderstorms were possible in the High Plains region of West Texas, and amended the outlook at 1:25 pm to include the possibility that some of the storms may become severe. Warm and dry conditions dominated the area throughout the afternoon; the temperature peaked at a high of 90 °F (32 °C) with moderate humidity. At 6 pm, large cumulus clouds began to appear in the area, and at 6:30 the first echoes indicating thunderstorms began to appear on radar scopes in nearby Amarillo. Less than half an hour later, Lubbock radar indicated the first thunderstorm activity in the immediate Lubbock vicinity: a moderate storm just south of the city near the small farming community of Woodrow.
Conditions continued to deteriorate through the early evening, and at 7:30 the local weather bureau issued a forecast which included the developing thunderstorm activity. By 7:45 the thunderstorm south of the city was indicated by radar to be increasing in intensity, and at 7:50 the National Weather Service issued a severe thunderstorm warning for Lubbock, Crosby and Floyd counties. Shortly afterward, reports of rapidly deteriorating conditions on the south side of the city of Lubbock began to come into the weather bureau and by 8:05, citizens south of the city were reporting golf ball-sized hail to the bureau.
At 8:10 pm, an off-duty Lubbock police officer spotted a funnel cloud on the east side of the city, and grapefruit-size hail was reported. At 8:15, local radar indicated a hook echo and a tornado warning was issued for Lubbock and Crosby counties, and the first tornado to strike the city touched down seven miles south of Lubbock Municipal Airport, near the intersection of Quirt Avenue and Broadway. Since it was in a relatively sparsely populated area of the city, this first tornado caused little significant damage; however, reports of damaging hail continued to come in from around the city. At 9:15, tornado sirens in Idalou were sounded, and by 9:30 baseball-sized hail was falling in the northeastern sector of Lubbock.
At about 9:35 pm, a second and much more significant tornado touched down near the campus of Texas Tech University, snapping light poles at Jones Stadium, home of the Red Raider football team, then began to track northeast, carving a path of destruction that at its peak reached almost two miles in width right through the heart of the city. The devastating twister tore through several densely populated residential areas before slicing through downtown, dealing a direct blow to the First National Bank building and the Great Plains Life building. The tornado then moved north toward the airport, where at 10:00 pm, anemometers were already reading winds of 77 knots (approximately 90 miles per hour (140 km/h). At 9:46, power failed at the Lubbock Civil Defense headquarters, and three minutes later, the local weather bureau lost power and its personnel took shelter from the tornado, which was now bearing down on the area and passed over the Weather Bureau building at 10:03 pm.
The tornado continued north-northeast toward the communities of Abernathy and New Deal, where local authorities had begun sounding tornado sirens due to alerts passed along to them via two-way radio by the officials at the crippled Lubbock Weather Bureau office. The tornado finally dissipated at about 10:10 pm near the community of Petersburg.
The second tornado was devastating, affecting a 25-square-mile (65 km2) area or roughly a quarter of Lubbock. Hardest hit were the inner city commercial and residential areas, the light industrial area south of Loop 289, and the residential area north of Loop 289 and the Lubbock Municipal Airport. A total of 430 homes were destroyed, 519 sustained major damage, and 7,851 more sustained minor damage. Some of the homes were completely swept away. Another 600 apartments were destroyed and 549 damaged, and one hundred mobile homes were severely damaged or destroyed. The Guadalupe neighborhood, consisting of mostly old wood frame or stucco homes, and parts of the Mesa Road area near the Lubbock Country Club, were almost completely leveled.
Since the tornado hit the downtown area, over 250 businesses were also severely damaged or destroyed, including 20 city and county offices. Every motel along 4th Street and Avenue Q north of 10th Street sustained major damage, and several motels and other businesses along Avenue Q, which is a major artery through the city, were destroyed. Several banks and warehouses were severely damaged, and one nightclub lost its entire top floor. Eight elementary schools were damaged, as well as Lubbock and Estacado High Schools, the latter losing a large portion of the roof over the gym. Damage was especially severe in the industrial areas of north Lubbock. At a grain storage complex, thick steel covers were peeled back from the tops of silos like soup cans. A 41-foot-long metal fertilizer tank, weighing 26,000 pounds, was thrown nearly a mile through the air. Large oil tanks in this area were hurled up to 300 yards away, and a railroad car was rolled for 50 yards.
The 271-foot-tall (83 m) Great Plains Life Building was left with a visible twist in its superstructure, leaving many to fear it was in danger of collapse; several radio towers on the roof were twisted or broken off. Much of the plaster in the stairwell walls between the 4th and 16th floors had cracked, and 60% of the building's windows were shattered. A foot of permanent deformation damage occurred at the steel frame on the south side, and three of the building's four elevators were damaged, with the support rails bent. In spite of the severity of the damage and amid cries to demolish, the owners chose to repair it instead, and it still stands. Some sources erroneously claim that the building was impacted by F5 winds. A thorough damage survey indicated that the F5 damage contour commenced farther north in the Guadelupe neighborhood.
In addition to damage to buildings, there was damage to other property. Over 10,000 vehicles were damaged or destroyed, and at Lubbock Municipal Airport, one hundred private aircraft and 19 military planes were destroyed. Many utilities were damaged or destroyed and 220 light poles were toppled, leaving the city's two utility companies scrambling to restore power in the days immediately following the storm. The Southwestern Bell Company reported that 25,000 telephones were knocked out of service and 600 long distance lines were ruined. There was extensive ecological damages as well; many trees were damaged or destroyed, including the city’s aged Chinese elm trees. Mackenzie State Park, Pioneer Park, Guadalupe Park and the Texas Tech campus lost almost all of their trees. Damage totaled $250 million, ($820,000,000 in 2015 dollars), making it the costliest U.S. tornado until it was surpassed by the Omaha Tornado of 1975.
The storm's final death toll was 26; victims ranged in age from 9 months to 88 years of age. Many of the victims were found in their homes, where they had been killed by flying debris or structural collapse. One boy lost his life when he was sucked out of the car he was riding in, and an entire family of five died when their house was lifted from its foundation, hurled over 200 yards, and slammed into a field. Another five hundred people were injured.
After the storm, Mayor Jim Granberry imposed a curfew, and Police Chief J.T. Alley issued orders that looters would be shot on sight. No looting was reported throughout the ordeal. The city council was directed to lead the rebuilding process, which continued under Granberry's successor, Morris W. Turner. The Lubbock Tornado also served as a model for the development of the Fujita scale, developed a year later. Bud Andrews and Ernesto Barton, Lubbock radio broadcasters, were given Presidential Citations from then U.S. President Richard M. Nixon for coverage of the disaster.