Timeline: How a late-night tornado unfolded in Naperville and Woodridge
The tornado that inflicted miles of damage in Naperville and Woodridge six months ago did not come without warning.
There were signs of trouble brewing "several days" before the tornado struck, said Brett Borchardt, a meteorologist at the Chicago office of the National Weather Service.
Here's how the night of June 20 unfolded.
The weather service issued the first tornado warning of the night for western DuPage County, roughly 19 minutes before it touched the ground.
Tornadoes develop with just the right mix of instability and changes in wind direction and speed.
"It started to become clear a few days in advance that we were going to have some of these very important conditions like vertical wind shear, warm, humid air at the surface, instability," said Victor Gensini, a meteorology professor at Northern Illinois University.
About 11:02 p.m.
The tornado touched down near Route 59 and 75th Street on the western edge of the Springbrook Prairie Forest Preserve. Meteorologists on teams surveying the damage the next day found shopping cart corrals were scattered on the east side of a Walmart parking lot, likely the beginning stages of what would turn into a tornado just off to the east.
A second tornado warning went out, covering southern DuPage and parts of western Cook County. There was already a warning in effect, "but for the majority of the tornado path from Woodridge eastward, the lead time was anywhere from 10 to 15 minutes," Borchardt said.
Commending the weather service, Gensini called the lead time -- how much advance notice is given before a tornado hits -- "very close to average, perhaps a little bit above average."
"You have to think that the early warning certainly let some people, especially in the middle of the night, to get up ... gather their belongings and get to a safe space."
At its strongest, the tornado roared across the Ranchview neighborhood just south of 75th Street. Winds peaked at around 140 mph, garnering an EF-3 rating on the zero-to-5 Enhanced Fujita scale.
The weather service assigned the rating based on a pocket of damage in the area around Princeton Circle, where the tornado reduced a two-story home to its foundation.
As it rumbled east, the tornado left homes in shambles, breaking windows, tearing off siding and roof shingles, uprooting and debarking trees. A blue sedan was tossed upside down like a toy car on 77th Street.
"A secondary area where it was near peak intensity was through Woodridge," Borchardt said.
Houses between Woodridge Drive and Basswood Lane took the brunt of the damage in Woodridge. The tornado tore apart Bridget Casey's home.
"It was just way too fast for me to even have a concept of time or anything," she said, still stunned days later.
"Very strong rotation and a very pronounced tornado debris signature up to at least 13kft over Darien, heading east," meteorologist Richard Castro wrote on NWS Chat, an instant messaging platform for relaying information to emergency managers.
Radar suggested the tornado lofted debris as high as 15,000 to 20,000 feet into the air.
About 11:25 p.m.
The tornado lifted south of the Des Plaines River in Willow Springs near the Tri-State Tollway. It stayed on the ground for almost 18 miles, injuring at least 11 people. A Woodridge woman lost her unborn child.
5:18 a.m. June 21
At sunrise, the light of a Monday morning revealed the full extent of the tornado's wrath.
It tore through densely populated areas at night, when tornadoes are often deadlier. But the weather service found mostly EF-2 damage along the tornado's path.
"We got very lucky," Gensini said.