Tomorrow (Friday) we will be marking 50 years since Northern Illinois’ worst tornado disaster, the April 21, 1967 tornado outbreak.
The winter of 1966-1967 had been a harsh one. In fact, it was a record setting winter. The record 23 inch snowstorm of January 26 and 27 led to Chicago’s snowiest winter, with a total of 68.4 inches. (The current record of 89.7 inches was set in 1978-1979). There was continuous snow cover on the ground from January 26 until March 9, a 42 day stretch! But the weather pattern had changed by late March and April. Spring had arrived. Chicago saw five straight days in the 70s the previous weekend – April 13 through 17. Rockford even hit 80 degrees during the mid-April warm spell. People in northeast Illinois were looking forward to another mild spring weekend Friday April 21.
Friday morning, April 21 a strong west-southwest upper level jet stream was in place from the southwest U.S. to the Great Lakes. At 500 millibars (about 18,000 feet) a short wave trough was moving rapidly northeast from the southwestern U.S. In response to the short wave, at the surface a wave of low pressure developed over the central Plains and moved northeast along a nearly stationary front which was draped across the Midwest. As the wave of low pressure approached northern Illinois, the stationary boundary surged north of Chicago as a warm front, bringing mild and humid air to the area. Temperatures climbed into the low to mid 70s across north and central Illinois on strong south winds and dew point temperatures reached the lower 60s. As the wave of low pressure approached during the warmth of the afternoon, surface winds backed slightly to the south-southeast. This likely increased the low level wind shear – the change of wind speed and direction with height – an important factor in producing rotating supercell thunderstorms and tornadoes. By late afternoon the mid level short wave was approaching and the upper level jet maximum of 120 knots (250 millibars or around 34, 000 feet) moved into the upper Great Lakes, which put northeast Illinois in the right-rear region of the jet – a favorable location for vertical development of thunderstorms.
This fatal combination of factors led to explosive development of rotating supercells along a line of storms that was moving across northern Illinois that afternoon. This line had already produced wind damage and tornadoes across Missouri, Iowa and northwest and north central Illinois. It would continue producing tornadoes across lower Michigan into the evening. But by far the most devastating tornadoes occurred in northeast Illinois and the Chicago area during the mid and late afternoon.
In the wake of the storms, much colder air poured into the area on northwest winds. Two days later northern Illinois had a very rare late April snow! A total of 3.8 inches fell at Rockford and 3.1 inches fell at Chicago (Midway) on April 23. This is the latest 3 inch snow on record for both locations.
The tornado first struck at 350 PM two miles southeast of Cherry Valley. The tornado passed the Chrysler plant near I-90 where 300 new cars and 100 employee cars were destroyed. The tornado continued east northeast through the southeast side of Belvidere. One hundred twenty seven homes were destroyed, and hundreds more were damaged. The most notable and horrific part of this tornado was the mayhem at the Belvidere High School. Buses had already picked up the elementary school children and were loading the high school students when the tornado struck. Twelve buses were rolled over. Students were flung like leaves into the muddy field. Thirteen of the 24 fatalities and 300 of the 500 injuries in this tornado occurred at the high school. According to Tom Grazulis of The Tornado Project, this was the nation’s sixth worst school death toll from a tornado. (Numbers one and two were also in Illinois – from the great Tri-State Tornado of 1925.) The tornado ended in McHenry County, about two miles north of Woodstock.
Tornado – BELVIDERE
Good article on the event on WREX http://addins.wrex.com/blogs/weather/2011/04/remembering-the-1967-belvidere-tornado