NOAA National Weather Service Weather Forecast Office

Severe Weather Outbreak of April 20, 2004

Several supercells developed across the northern third of Illinois the afternoon of April 20, 2004, continuing into the evening across northeast parts of the state. 

The tornadoes detailed on this page affected Stark and Marshall Counties, within the coverage area of the Lincoln NWS office.  Additional information on storms near Granville can be found at the Quad Cities NWS page, and the Utica and Joliet tornado information is available at the Chicago NWS page (PDF format).  There were also 12 tornadoes across central and northern Indiana and is covered by the Indianapolis NWS Page and North Webster NWS Page.  The Storm Prediction Center (SPC) has an analysis of the tornadic outbreak across northern IL and IN on April 20.

If you have any photos of the tornadoes or damage you wish to share, please send an E-mail to the Lincoln NWS Webmaster.

This page is divided into 3 sections:  Specific tornado tracks, weather and radar images, and photos.

Here is a Case Study of the April 20, 2004 Tornadic Event in Illinois.

Stark and Marshall Counties (click image to enlarge)

NWS personnel surveyed a tornado track which crossed the Stark/Marshall county line near Camp Grove.

This tornado touched down approximately 1.2 miles west-southwest of Camp Grove, just south of the intersection of Highway 17 and Highway 40 in eastern Stark County.  The tornado was on the ground for 1.8 miles, lifting approximately 0.8 miles north of Camp Grove at county road 1150N.  The tornado was rated as intensity F1, with winds estimated between 75 and 80 mph.  It was 50 yards wide.

The tornado broke 5 windows at a house and damaged a barn roof on IL-17 just east of the IL-40 intersection.  It also uprooted one tree, and snapped 3 other ones off.

No deaths or injuries were reported from this tornado.

Marshall and Bureau Counties (click image to enlarge)

Another tornado touched down shortly after the first one lifted.  It started 2.5 miles northeast of Camp Grove, just east of the intersection of Western Ave. and county road 150E.  It moved east-northeast across the Saratoga Center area and crossed into Bureau County about 1/2 mile west of Whitefield.  The tornado traveled an additional 1.5 miles into extreme southern Bureau County, lifting about a mile northeast of Whitefield. 

This tornado was on the ground for a total of 7.5 miles.  It was rated F1 with maximum wind speeds estimated at 110 mph, and was about a quarter mile wide at its strongest.

The tornado destroyed a shed and pole barn with farm equipment worth nearly a quarter million dollars at Saratoga Center (county roads 1300N and 250E).  Numerous trees and power lines were blown down, and a large grain bin was blown into a field.

The parent storm later produced a strong tornado at Granville, in Putnam County.  Information on this area can be obtained from the Quad Cities NWS office.

Weather and Radar Images (click to enlarge):
 

	This image shows the surface map across northern and central Illinois at 4 pm CDT (21Z).  Surface-based lifted index values are indicated by the blue lines, and surface-based CAPE is indicated by the shaded areas.
	A mosaic radar image of northern and central Illinois at 3:54 pm CDT.  The only storm of interest at this time is between Quincy and Springfield, near Beardstown.
	A mosaic radar image of northern and central Illinois at 4:36 pm CDT.  Storms were intensifying across the middle Illinois River Valley, with the strongest storm just south of Havana.
	This image from the Lincoln radar at 4:45 pm CDT indicates a possible tornadic supercell near Havana.  (No reports of tornadoes in this area have been received.)
	Further north, the Quad Cities radar at 5:04 pm shows a circulation along the Stark and Marshall county line in this Storm Relative Motion velocity image.  A tornado touched down in this area (see description at the top of the page).
	At 5:15 pm, the Quad Cities radar indicates that the circulation is now centered over northwest Marshall County west of Henry.  A tornado touched down around this time 2.5 miles northeast of Camp Grove, later moving into Bureau County.
	A mosaic radar image of northern and central Illinois at 4:36 pm CDT.  Supercells are indicated south of Peoria and southwest of La Salle, with additional strong storms developing southeast of Bloomington.
	The Quad Cities radar at 5:40 pm showed that the tornadic supercell from Stark and Marshall counties was located in northern Putnam County, approaching the town of Granville.
	Storm relative motion velocity image from the Quad Cities radar at 5:40 pm.
	A look at a mosaic radar image from 6 pm shows numerous strong to severe thunderstorms across northern and central Illinois.  The most severe storm was in western La Salle County.
	By 6:54 pm, most of the strong to severe storms were affecting the northeast quarter of Illinois.