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Cold Front Dropping South Across the Western U.S.; Watching Threat for Tornadoes and Flooding in the South

A cold front will push south across the Western U.S. into Tuesday with mountain snow and areas of gusty to high winds. An area of low pressure will form along this front on Tuesday and bring a potential for severe thunderstorms with tornadoes and excessive rainfall in the lower to mid Mississippi River Valley. To the north, heavy snow is possible in parts of the upper Midwest. Read More >

On April 19, 1996, Illinois recorded its largest tornado outbreak on record. Across the state, 39 tornadoes were observed.  These tornadoes were part of a larger outbreak across the Midwest. 

Tornado reports from 7 am April 19 to 7 am April 20

Four of these tornadoes occured in the forecast area covered by the NWS office in Chicago (also known as its 'County Warning Area' or CWA).  A tornado in Zion rated F2 on the original Fujita Scale produced significant damage and resulted in two injuries. 

The Zion tornado was somewhat unusual in multiple respects.  First, as seen in the map above, it was by far the most northern of all the tornadoes during the event.  It also was by far the latest tornado during the event, occurring about two hours after the previous tornado.  Additionally, the tornado was rated as F2 which is considered a strong tornado, yet it was very short lived and occurred as part of a bowing line of storms rather than from an isolated supercell, as seen in this loop of Doppler radar Reflectivity (left side) and Base Velocity (right side):

Radar loop of Zion, IL tornado

 

4/19/1996 Tornado Summary for NWS Chicago County Warning Area

Location County F-Scale Time (CST)  
Rutland LaSalle F1 4:40-4:41 PM More information
Herscher Kankakee F0 5:25-5:29 PM More information
Momence Kankakee F0 6:01-6:08 PM More information
Zion Lake, IL F2 10:32-10:35 PM More information

 

Most of the Illinois tornadoes on this day occurred in areas covered by other National Weather Service offices.  Here is some additional information about the event from those offices: