• A tornado outbreak occurred across portions of Iowa, Illinois, and Indiana on April 20, 2004. In total, 29 tornadoes occurred, with 16 of those in Illinois and 12 of those in the NWS Chicago forecast area (listed below).

• The most notable tornado of the event was the F3 that hit Granville and North Utica, IL, killing 8 people.

Tornadoes that occurred in the NWS Chicago forecast area:
1.) Granville - North Utica F3
2.) North Utica - Ottawa F2
3.) Wedron F1
4.) Sheridan F0
5.) Piper City F0
6.) Piper City/Ashkum F0
7.) Channahon F0
8.) Hopkins Park F2
9.) Kankakee F1
10.) Joliet F1
11.) Grant Park F0
12.) Beecher F0

Summary: 

This tornado started just north-northeast of Florid and moved northeast toward Granville. The tornado widened to an approximately 1/2 mile wide, multi-vortex tornado as moved through Granville. Damage occurred to numerous buildings, including the elementary school. Additional information on the Putnam County portion of the tornado can be found on NWS Quad Cities' summary web page for this event.

The tornado continued northeast, eventually crossing the LaSalle County border and producing F0 intensity damage in a wooded area southwest of Peru. As the tornado continued northeast, several homes in a subdivision near the intersection of East 250th and 2569th Roads suffered F2 damage, having their roofs blown off and suffering damage to external walls. Significant tree damage occurred as well. Path width was estimated at 50 yards at this location. The tornado then continued northeast, crossing the Illinois River twice as it moved toward the town of North Utica, downing a steel high tension tower on the north bank of the river, immediately west of IL-251. The tornado moved into the southwest side of North Utica while it was at F0 intensity. The tornado rapidly increased to F3 intensity on the north side of Johnson Street, where one home had its roof taken off and north walls blown out. A machinery building was completely destroyed on the south side of the canal, and a semi-tractor trailer was blown into the canal. The tornado then moved north of the canal into the heart of town where several homes were severely damaged, garages were destroyed, and brick buildings collapsed. Eight people died and seven were rescued from the basement of a tavern. On the east edge of the vortex along Mill Street, in downtown, buildings suffered damage to facades, roofs and windows. The tornado crossed the railroad tracks and  dissipated on a steep bluff on the northeast side of town.

Summary: 

The tornado formed on the ridge northeast of Utica and moved across County Road 2803, west of 10th Street. A garage was destroyed and trees were damaged. The tornado became a wide multiple-vortex tornado and caused damage to two homes, trees, and outbuildings on Route 6, west of 11th Street. Part of the roof of a house was torn off. A storage building was damaged and a garage roof removed on 11th Street. A garage and grain bin were destroyed on County Road 2950. The tornado crossed I-80 at 12th Street, damaging a building and flipping a semi-tractor trailer. The tornado destroyed a machine shed on 13th Street and knocked down power poles. On 31st Street west of 14th Street, big pine trees were snapped and a house suffered roof damage. A barn was destroyed on 14th Street north of 31st Street. On 32nd Street west of 15th Street, a two story house was hit. The top floor was mostly destroyed. A machine shed was destroyed on 16th Street between 32nd and 33rd streets. The tornado ended at 33rd Street and Route 23, where there was minor tree damage.

North of I-80, a small satellite tornado formed behind the large parent tornado. It had a damage path 2 miles long and 5 to 20 yards wide. Its track was about 1/4 to 3/4 mile south of the main track. It caused no damage.

Summary: 

The tornado began in an open area west of town. It knocked over a camper at a house, snapped pine trees and blew over a shed. The tornado struck a detached garage, completely destroying it. Trees were also damaged.

Summary: 

The tornado was spotted by a storm chaser near the correctional facility south of Sheridan. It tracked northeast for about 2 miles, causing only minor tree damage.

Summary: 

The tornado occurred briefly at a farm north of Piper City, damaging a grain bin and an outbuilding.

Summary: 

A weak tornado originated in Ford County 9 miles north-northeast of Piper City and moved into Iroquois County, ending about 9 miles west of Ashkum. This tornado moved through open farm land and caused no damage.

Summary: 

The tornado struck an industrial complex on the far west side of Channahon. A wastewater treatment building at Tabler Road, south of Route 6, was destroyed with its walls getting blown out and structural beams getting bent. There was damage to overhead doors, and an air handling unit was torn from a roof of a building on the east side of Tabler Road. Farther to the east, there was damage to the walls and roof of an outbuilding. Antennas were blown down at the fire station on Route 6.

Summary: 

The tornado began in an open field and moved north-northeast along County Road 11000 East, knocking down trees and limbs. The tornado intensified from County Road 2630 South to 2430 South, where homes were damaged, a mobile home was destroyed, and large trees were knocked down or damaged. The most intense damage occurred at a church, where the roof was taken off and walls were pushed down. The tornado continued across a farm field, knocking over 2 pivot irrigation systems. It ended near 1000 South, where trees were damaged.

Summary: 

This tornado formed just southwest of the intersection of County Roads 5000S and 3000W. Eyewitnesses stated there were multiple funnels aloft occasionally lowering at this point. The developing vortex continued northeast across 3000S just west of 1000W. A brick one story house was was hit with the roof torn off and scattered northeast into a field across the street. Numerous large trees were snapped or uprooted. An empty corrugated grain bin was pushed into a tree. The tornado continued northeast, damaging the brick wall of a chemical plant and damaging a chain link fence. Several cinder block buildings were damaged or destroyed in this complex. The vortex moved across railroad tracks and damaged corrugated metal roofs at the River Valley Metro building (city bus storage) and other nearby businesses. The final damage occurred at a farm at the corner of US-45/US-52 and River Road. A barn and several large sheds were destroyed. The tornado lifted as it moved just west of Kankakee Community College to the Kankakee River. Areas of debris could be seen in the trees north of River Road, but no tree damage was noted.

Summary: 

This brief tornado moved through a mainly residential area just west of downtown Joliet. Initial damage was found near the intersection of Jefferson St. (U.S. Route 52) and William Street. The damage path then continued northeastward to a point near the intersections of Ruby Street, Bluff Street, and the Des Plaines River. Most of the damage was of F0 intensity, with extensive tree damage and very minor damage to structures. However, there were three pockets of more substantial primary structural damage, which consisted mainly of roofs being torn off residences and garages being totally demolished. In all, 10 residences were declared uninhabitable.

Summary: 

This tornado began about 1 mile southwest of Grant Park in an open field, where it was spotted by the fire department. It crossed Route 1 west of town, damaging a fence. The tornado moved into town, causing minor roof damage to a few homes. Part of the roof of the fire station was peeled off, and a large tree fell in the yard behind the fire station. The tornado moved across an open field, then knocked down a large tree at 9000N and Route 1. It also caused minor roof damage to a farm building northeast of the intersection.

Summary: 

A weak tornado pulled shingles off two mobile homes near the corner of 319th and Yates. It also caused minor roof damage to a barn.

Radar loop for April 20, 2004

Radar imagery while the Granville-Utica tornado was occurring.

Weeks after the event, meteorologists in the weather enterprise (that included NWS Chicago forecasters) researched the quickly changing and deceptive tornadic environment.  Their technical assessment can be found to the right. 

The rapidly warming and moistening atmosphere during the mid to late afternoon across north central Illinois created instability that was sufficient for thunderstorms. The focus for these storms was along an evolving warm front which was surging northward.  This type of boundary is often favorable for rotating storms and low cloud bases, both ingredients for potential significant tornadoes. Many of the weather forecast models struggled with this scenario, however, and indicated little-to-no instability. At first, weather observations early in the afternoon matched this prediction.  The warmer airmass in southern Illinois raced northward through the day, combining with morning rain, to further moisten the atmosphere. This helped support low cloud bases and possible tornadoes.