The powerful supercell that produced a tornado that damaged one town and smashed another was most likely the one that triggered dire warnings for Marengo and central McHenry County that, fortunately, did not come to pass.
That system produced a large tornado Thursday night that one of McHenry County’s trained spotters – one of the “most reliable” that Emergency Management Agency Director David Christensen says he has – reported at about 7:40 p.m. near Route 20 and Johnson Road between Marengo and Garden Prairie.
Several minutes earlier, the National Weather Service had issued an immediate warning based on its Doppler radar data telling people in Marengo that, "You are in a life-threatening situation." A local resident who chases storms as a hobby likewise told the Northwest Herald that the tornado was a large wedge-shaped one.
Earlier, the storm destroyed 30 homes and destroyed a restaurant in Rochelle in Ogle County, and went on to level unincorporated Fairdale in northwestern DeKalb county, killing two and injuring at least seven. The weather service has tentatively classified that tornado as an EF-4, the second-highest rating, packing winds between 166 and 200 mph.
But for whatever reason, the tornado that was headed for Marengo petered out.
Although the storm was one of at least two tornadoes that hit McHenry County, the other near Harvard, Christensen said damage reports have not amounted to much beyond some siding, a dead chicken, and a handful of power outages.
“I’ve been doing this for a long time. I’ve never seen anything like this,” Christensen said.
Several disaster teams from the National Weather Service were moving Friday through north central Illinois to ascertain damage in two distinct tracks from Ogle and Lee counties through Winnebago, DeKalb, Boone and McHenry counties. The southern track produced the Fairdale tornado, while the northern one produced a tornado near Harvard.
“The questions the teams are trying to focus on are, was [damage caused by] one tornado? Was it multiple? Did one lift and the storm dropped another?” National Weather Service forecaster Jamie Enderlen said.
A helicopter survey conducted early Friday afternoon found no damage along either path, Christensen said.
"Everybody's scratching their heads over this. Even the weather service," he said.
The storm system that smashed Fairdale but spared Marengo kept going and prompted warnings for Woodstock and McHenry, both of which received large hail.
While Christensen said he is very happy that McHenry County was spared, he hopes that that fact does not mean that people take warnings less seriously the next time severe weather threatens the area. Peak tornado season in Illinois is April through June – Saturday is the 50th anniversary of the Palm Sunday Tornado that ripped through Crystal Lake.
“When the warnings go out, we’re serious. Something was on our side last night, but that doesn’t mean we’re going to luck out next time,” Christensen said.