Meteorological Synopsis
| State | Total | County | County total |
|---|---|---|---|
| Illinois | 58 | Boone | 24 |
| Cook | 33 | ||
| Lake | 1 | ||
| Totals | 58 | ||
April 21, 1967, was a warm Friday afternoon in northern Illinois. A warm front part of a very deep storm system had been marching through Illinois all day and by afternoon moved north of the state. Temperatures ahead of the storms into the low to mid 70s°F with dewpoints in the 60s°F, an upper-level jet reaching 120-knot (220 km/h), and increasing low-level shear. By 3 P.M., more than 12 tornadoes had already been spawned from the storm system. The National Weather Service was able to issue a tornado watch at 1:50 P.M.
Read more about this topic: 1967 Oak Lawn Tornado Outbreak