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1967 Oak Lawn tornado outbreak

F4 tornado
Max rating1 F4 tornado
1Most severe tornado damage; see Fujita scale

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.


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