The 1967 Oak Lawn tornado outbreak was a destructive tornado outbreak and severe weather event that occurred on April 21, 1967, across the Upper Midwest, in particular the towns of Belvidere and Oak Lawn, Illinois. Locally known as 'Black Friday,' it was the largest tornado outbreak of 1967 and one of the most notable to ever occur in the Chicago metropolitan area. The outbreak produced numerous and significant (F2+) tornadoes, with ten of them in Illinois alone. Included was one of just six documented violent (F4/F5) tornadoes in the Chicago metropolitan area since the area was first settled. Meteorological synopsis 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 , 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. Confirmed tornadoes Belvidere, Illinois The F4 tornado that struck the Belvidere-Lake Zurich area was responsible for one of the highest tornado-related death tolls in a single school building ever recorded when it struck Belvidere High School as multiple school buses were being loaded. At 3:50 P.M., a violent multiple vortex tornado, later given an F4 rating, moved through Belvidere, Illinois, damaging the high school and overturning buses. A total of 24 people were killed with 13 them of dead in Belvidere at Belvidere High School, making this tornado the sixth deadliest ever to hit a school. 410 people were injured as well and 127 homes destroyed with another 379 being damaged. Seven people were also killed at a shopping center. The Belvidere tornado was especially devastating because it hit the school