Weather records, like baseball statistics, pile up fast– daily highs, innings pitched, dew points, runners advanced. There are plenty of them, but they don’t amount to much.
Every now and then a real slugger comes along, a legend people will talk about for generations to come. So it was that the Babe Ruth of summer storms swept into the area Wednesday afternoon, unloading a record 16.91 inches of rain on Aurora by Thursday morning.
That is a real record, the all-time, 24-hour deluge for the state of Illinois, just a few notches short of the national mark for torrents, 19 inches that fell in Alvin, Texas in 1979.
How much havoc can so much water create? Enough to send police out in boats in Orland Park and Lisle to rescue more than 100 stranded people.
Enough to chase thousands out of their homes, and keep tens of thousands more inside, as it shut down a Metra west suburban rail line and parts of Interstates 88 and 55. Electric power and telephone service failed over wide areas.
In Cook County, where the rain was not as heavy, the Metropolitan Water Reclamation District quickly filled its billion-gallon Deep Tunnel, designed to hold the overflow of storm water and sewage.
To keep the Chicago River from overflowing, the district opened the river’s locks and dumped hundreds of thousands of gallons of water containing raw sewage into Lake Michigan.
Thirteen northern Illinois counties were declared disaster areas. Gov. Jim Edgar put the National Guard on alert. Damage was estimated in the hundreds of millions of dollars.
The odd thing about this ark-building rain was that it came from a rather average storm system, meteorologists said. The low pressure cell was no bigger, no more violent, than a typical summer low.
The distinguishing feature of this system, meteorologists said, was that it was slow.
So slow, in fact, that the warm front triggering the storms stalled over northern Illinois Wednesday. Thunderstorm after thunderstorm developed along the same east-west line, stretching roughly from Rockford to Joliet.
Meanwhile, upper atmosphere winds–10,000 to 20,000 feet aloft–happened to be cruising parallel to the front, pushing each of those storms along the same track, an effect called “train echo.”
And the end of the line was Aurora. If anything, the 16.91-inch measurement was conservative. Doppler radar showed 17.2 inches of rainfall in Aurora.
At first, the storm didn’t look like much to forecasters.
“Then, after you see three, four, five storms go to the same location, that’s when you say, `Uh-oh, that’s trouble,’ ” said staff meteorologist Richard Brumer of the National Weather Service.
This month’s record rains, last July’s record heat, the very long and gloomy spring make some people wonder whether the region is experiencing long-term climate changes or just freak events.
Climatologists say it is difficult to tell, although some studies have shown that major storms are becoming more common.
“What may have been a five-year storm before now occurs every two years, and that’s a very significant change to us,” said Ken Kunkel of the Midwestern Climate Center in Champaign.
Measured over 150 years, a pittance in climatic terms, what those changes signify remains open to interpretation.
“Can this be connected to some driving force for climate change? That’s a question that’s hotly debated among climate scientists at the present time,” said Ronald Prinn, director of the Center for Global Change Science at the Massachusetts Institute of Technology.
“It can’t be ruled out. It is a possible explanation,” he said. “But the most likely explanation for these trends is simply that the climate system at the regional level is variable on a decade-to-decade, century-to-century time scale.”
Weather records in much of the United States are about a century old. In Illinois, the oldest records date to the 1840s, but those are just for Chicago. In much of the rest of the state, written records do not exist before the late 1800s.
“Without knowing what the natural variation is at the regional scale (over centuries), it’s difficult to answer the question: Is this due to some underlying force, such as the rise of greenhouse gases?” said Prinn, a chemist who studies climatic change. Some climate models show that if global warming is occurring, interior continental areas like the Midwest are likely to endure droughts, not floods.
But those models are imprecise, and especially poor at simulating extreme weather patterns such as heat waves and floods.
Predicting record storms on a shorter time scale–including the nightly forecast–also is difficult.
“A forecaster would be crazy to forecast a record,” said Wayne Wendland, climatologist with the Illinois State Water Survey in Champaign. “If it hasn’t happened in 100 years, why would it happen tonight? But occasionally, it does.”
And if a forecaster could pinpoint the day, how about the place? Wednesday night’s storms were highly selective in their targets. Aurora’s record 16.91 inches was measured at the Water Treatment Plant, but in neighboring Wheaton there was less than half that much, 7.24 inches.
Moving away from the front, Midway Airport tallied 7.69 inches, while O’Hare International Airport measured a relatively paltry 2.36 inches.
Relativity, of course, is everything here; Hurricane Bertha never dropped more than 8 inches of rain on any single spot in the United States last weekend. And even a single inch of rain over Cook County amounts to 15 billion gallons of water.
Moreover, the effects felt by people have as much to do with the landscape below as the clouds above. Fifty years ago, a storm line stretching from Rockford to Joliet might have soaked mostly fields. Now the rain falls on roads and parking lots, houses and carefully graded lawns.
That concentrates waters in the lowest available empty places. In a mild rain, it goes to culverts and sewers. When those fill up in a heavier rain, the water seeks out low spots in streets, basements and eventually the ground floors of homes and businesses.
In Joliet Thursday, more than 8,000 homes had been flooded, along with 100 roads. Nearly all the smaller, surrounding communities reported hundreds of flooded homes each.
Chicago reported 3,000 flooded basements Thursday evening, and has stepped up the testing of drinking water to ensure the untreated sewage in the lake does not contaminate the supply. Beaches will be closed until at least Friday afternoon in Chicago, although there have been no reports of contamination.
Evanston, Wilmette and Lake County officials were also considering closing beaches under their jurisdiction.
Rivers and streams, meanwhile, continued to inch toward flood stage Thursday evening.
The Fox, DuPage and Des Plaines Rivers were all expected to crest sometime Friday.
One death was blamed on the storm. The Will County Emergency Management Agency reported that an 84-year-old Joliet man who had a history of heart problems had suffered a fatal heart attack while trying to salvage possessions from the basement of his home. The agency declined to identify the man.
“It is definitely a disaster and the major thing we can hope for at this point is that the rain won’t come back and we can begin the cleanup process,” said Edgar.
Edgar said that when he had collected enough information, he planned to ask the region to be declared a federal disaster area.
Commonwealth Edison expects that 2,500 or more people may still be without power Friday morning, further delaying cleanup. At the height of the storm, 27,500 people were without electricity.
Commuter rail officials said they would work throughout Thursday night to clear tracks of mud and debris, in hopes of getting some 40,000 displaced passengers back on track.
But a spokesman urged commuters to listen to broadcast reports Friday morning because the west line may not yet be open.
The forcecasts for Friday and Saturday are for dry conditions, but clouds may begin to creep in again Sunday.
It is, after all, the thunderstorm season, fueled by moisture from the Gulf of Mexico, stirred by upper-level winds and triggered by the daily baking of the Earth by the sun.
Illinois forecasters have tried to discern predictable patterns for weather by studying unusual seasons–for example, the summer following a record cold spring, or the fall after a record hot summer.
“We looked at all the seasons plus all the characteristics,” Wendland said. “We didn’t learn a thing. The person who plays the odds game would say, `Since we’ve had so much rain now, we’ll likely have less through the rest of the summer,’ ” he said.
“Maybe. But you can’t bet on it.”
