The 1967 Oak Lawn tornado outbreak was a destructive tornado outbreak and severe weather event that occurred on April 21, 1967, across the Upper Midwestern United States, in particular the Chicago area including the towns of Belvidere and Oak Lawn, Illinois. It was the most notable tornado outbreak of 1967 and one of the most notable to occur in the Chicago area. The outbreak produced numerous significant (F2+) tornadoes, among them eight alone in the U.S. state of Illinois, including one of just six documented violent (F4–F5) tornadoes in the Chicago metropolitan area since the area was first settled. The F4 tornado that struck Belvidere caused one of the highest tornado-related death tolls in a single school building and was featured in an episode of The Weather Channel's Storm Stories.
April 21, 1967, was a warm Friday afternoon in northern Illinois. Following a foggy morning with temperatures in the middle 50s°F, temperatures rose rapidly in the afternoon as low geopotential heights approached from the southwest. A warm front—part of a very deep shortwave trough—passed through Illinois all day and by afternoon moved north of the state. As a low pressure area within an extratropical cyclone approached the area, temperatures rose into the low to mid 70s°F with dew points rising into the 60s°F, an upper-level jet reaching 120-knot (220 km/h), and increasing low-level vertical shear. Meanwhile, a persistent mesolow feature near Joliet, Illinois, helped to maintain backed low-level winds from the south. As conditions became more favorable for tornadoes and supercells began developing in the Chicago area, the regional U.S. Weather Bureau office issued a tornado watch at 1:50 p.m. CDT covering the northern half of Illinois plus southern Wisconsin, eastern Iowa, and western Indiana. By 3 p.m. CDT/2100 UTC, more than 12 tornadoes had already been spawned from the storm system.
At 3:50 P.M., a violent multiple vortex tornado, posthumously rated F4, moved through Belvidere, Illinois, damaging the high school and overturning buses. Twenty-four people were killed and another 410 injured with 127 homes destroyed and 379 damaged. Thirteen of the 24 people killed in Belvidere were killed at Belvidere High School, making this tornado the sixth deadliest ever to hit a school. Seven people were also killed at a shopping center. The Belvidere tornado was especially devastating because it hit the school just as students were getting on the buses to go home. Just before 4 p.m. CST, the tornado reached the school. Twelve buses, already filled with elementary- and middle-school students, were tossed about. Several of the students were tossed into adjacent fields and killed. A bus driver was killed as well. Shortly after the passing of the tornado, faculty and some of the stronger students used the fireproof doors of the high school as stretchers to carry the injured into the cafeteria, the severely injured into the library, and the dead into the gymnasium. Three hundred new cars and 100 employee cars were destroyed at the Chrysler plant in town. A school bus driving south of Harvard was thrown into power lines and torn in half. The driver and students survived by sheltering in a ditch.
The second violent tornado of the day in Illinois may have developed as far southwest as Elgin, but was first observed at about 5:00 p.m. CDT near Fox River Grove, though its path is officially believed to have begun near Middlebury. It then produced a discontinuous damage path through Fox River Grove, North Barrington, and Lake Zurich. The most intense damage, posthumously rated F4, occurred at Lake Zurich Manor, about 1.5 miles (2.4 km) northwest of downtown Lake Zurich; there, roughly 75 homes were leveled and 200 severely damaged. The Acorn Acres subdivision, northeast of and adjourning Lake Zurich Manor, reported scattered damage and debris with about 12 homes severely damaged. According to official plots from Storm Data, the tornado lifted after hitting Acorn Acres, though non-tornadic damages to trees and buildings occurred as far as the intersection of Illinois Route 63 and Gilmer Road. There, severe winds, possibly downbursts, destroyed four homes, one brewery, and a plastic-manufacturing site, though at least one source indicates that the tornado was likely still present at that place. In all, the tornado damaged 400–500 homes and destroyed about 100. An air-conditioning unit weighing 1,000 lb (16,000 oz) was thrown .5 mi (0.80 km). Cars were picked up and tossed as well.
The third and final F4 tornado to affect Illinois this day was also the deadliest tornado of the entire outbreak. An intense supercell with a hook echo on weather radar first appeared about 18 miles (29 km) west-northwest of Joliet at 4:45 p.m. CDT. Later, at 5:15 p.m., an employee of the U.S. Weather Bureau observed a rotating wall cloud about 10 miles (16 km) north of Joliet. Minutes later, severe thunderstorm winds blew out windows in a building, though no tornado or funnel cloud had yet occurred. Near the Little Red Schoolhouse, in what is now the Forest Preserve District of Cook County, an observer first noted a funnel cloud to the south, moving east with hail up to .75 inches (19 mm) in diameter—but he was unable to report to the Weather Bureau as his telephone failed to give a dial tone. At 5:24 p.m. CDT, a tornado touched down at the present-day campus of Moraine Valley Community College and moved east-northeast, mainly at 70° heading. As it touched down, the tornado bent power poles and blew down small trees and vegetation, tossing dirt as it went. It then grew in size to 450 feet (150 yd) wide and entered Palos Hills, destroying about five buildings—including two frame homes and a brick home—and snapping trees. Subsequently, the intensifying funnel severely damaged homes and a drive-in theater in a half-block-wide area of the Chicago Ridge.
Over the next six minutes, the tornado attained its maximum intensity as it tore a 16.2-mile (26.1 km) (60-mile-per-hour (97 km/h) ground speed) swath of damage through Oak Lawn, Hometown, and Evergreen Park. As it passed through the business district of Oak Lawn, the tornado leveled many homes that were built entirely of brick. In Oak Lawn, the tornado threw 25–40 vehicles from the intersection of Southwest Highway and W. 95th St. (US-12/20), killing 16 people who were stuck in traffic during the rush hour. Partly for that reason, this tornado ended up being the deadliest in the outbreak. As it moved beyond Oak Lawn, the tornado weakened and widened as it caused lighter damage to vegetation, roofs, and garages. It finally moved offshore as a waterspout at Rainbow Beach, producing a wind gust up to 100 miles per hour (160 km/h) at a water filtration plant on the lakefront shore. In all, the tornado killed 33 people, including several children at a roller skating rink, and injured 1,000. It destroyed 152 homes and damaged 900, causing $50 million in damage. The destroyed buildings included a high school, grocery store, tavern, market, motel, drive-in theater, restaurant, numerous apartments, and two gas stations. Additionally, the tornado caused numerous fires in Oak Lawn which were quickly extinguished.
Two days later on Sunday, April 23, 1967, three inches (76 mm) of snow fell on Belvidere, which only exacerbated the cleanup from Friday's tornadoes. In fact, many cities and towns in the Midwest broke record overnight lows on April 24 and 25. A state of emergency was declared for Boone County, and the reserves came to assist in the cleanup effort.