Don Robertson, whose Plainfield home was tousled by high winds but escaped destruction when a 1990 tornado swept through that community, knows a twister when he sees one.
But detecting the seeds of a tornado, the very early signs marching across a horizon already filled with odd and shadowy shapes, might be quite another matter.
”Now I know where to look and what to look for,” Robertson said Thursday after he and more than 40 other Will County Highway Department workers got a crash course as tornado spotters in the area that has become infamous as a tornado alley.
”I know to look for the wall cloud and (how) not to confuse a funnel cloud with a downpour of rain,” Robertson said confidently.
Many of these same workers who sat in the rows of folding chairs in Highway Department headquarters southeast of Joliet were among the rescue teams dispatched to Plainfield in the hours following the 1990 storm.
The group gathered in a darkened conference room to watch deadly twisters develop on slides and film while a representative of the U.S. Weather Service pointed to a succession of tornado look-alikes, as well as some examples of the genuine article.
”We want you to know what you are seeing,” said Jim Allsopp, a weather service meteorologist, who specializes in tornado warnings. ”We will be depending heavily on what you tell us.”
False reports, he said, are nearly as bad as failing to issue a legitimate warning.
”People become complacent when they hear the sirens going off every day,” he warned.
The new group of spotters will supplement a growing army of volunteers in Will County who have been trained to watch an approaching thunderstorm and focus on the ”wall cloud” at its base, looking for the tell-tale rotation that separates a summer downpour from a killer storm.
”Sometimes it`s very difficult to tell the difference,” Allsopp said.
”The rotation is the key. A tornado is a violently rotating column of air that forms in a thunderstorm and comes in contact with the ground.”
A funnel cloud remains airborne, often waiting to become a tornado.
”You will have a highly developed, well-organized rotation,” he emphasized.
Like a surgeon guiding interns` eyes to the heart amid the gore, Allsopp pointed to the center of one of nature`s deadliest engines.
There, he said, is the wall cloud, a drooping mass hanging from the towering, energy-packed clouds of the thunderstorm. To one side of the wall cloud will be a dark rain cloud reaching to the ground, and on the other a rain-free band.
It is near the wall cloud that the warm, moist air that fuels the storm is swept upward and where the tell-tale funnel cloud usually is born.
The trick, said Allsopp, is to distinguish between a genuinely rotating funnel cloud and a cast of imposters, including streams of rain and an array of other cloud formations that have no special meaning.
Allsopp, whose Romeoville offices are in an area that has come to be regarded as tornado country because of two recent storms in Plainfield and Lemont, cited figures showing that the nation`s true tornado alley is situated in the broad expanse of open plains west of the Mississippi River.
But, he said, the Chicago area still is a high-risk sector and has hosted some of the deadliest storms in U.S. history.
A 1925 storm took nearly 700 lives in three states including Illinois, while a tornado on Palm Sunday in 1965 left 272 dead, including a heavy toll in Crystal Lake, Allsopp pointed out. In April 1967, 50 were killed in eight states, including 32 in southwest suburban Oak Lawn. That storm also ripped through Belvidere and Lake Zurich.
But Allsop said, contrary to popular perception, tornadoes have been evenly distributed throughout the metropolitan area and have no real statistical home.
But most tornadoes, he told the group, occur in June and move from southwest to northeast, striking between 2 p.m. and 9 p.m.
These probabilities provide little shelter to anyone in the path of a tornado, however.
The Plainfield tornado that took 29 lives in August 1990 had only the time right-3:30 p.m.
Harold Damron, deputy director of Will County Emergency Services, said the highway workers are the second group of county employees to be trained in the ways of tornadoes and will be especially valuable to the warning effort, even with the expected installation next March in Romeoville of advanced Doppler radar, which will allow forecasters to identify twisters earlier than now possible.
It`s the spotters, said Allsopp who provide the information that turns a tornado watch into a warning to take cover.
”It`s very hard for us to see a tornado on radar,” he said. ”We really don`t know if there`s a tornado on the ground until somebody calls in and says there is.”
”And maybe now,” he said of his new spotters, ”they won`t be fooled by those ragged clouds on the leading edge of a storm.”
