The line of supercell thunderstorms that moved through northern Illinois and northwest Indiana Tuesday night brought nearly 70 mph wind gusts, golf ball- to baseball-sized hail, and an inch of rain.
It also temporarily left 50,000 customers without power and damaged a school in the Minooka area, where forecasters think a tornado may have formed.
The thunderstorms were supercells, or storms with rotating updrafts, according to the National Weather Service. “Supercells are known for producing all hazards of severe weather (damaging hail, winds, and tornadoes), and develop in environments with strong wind shear,” its website said.
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Meteorologists also said “the damage from Minooka to Channahon may be partly due to a brief tornado,” and the agency had sent members of its storm assessment team to the area — about 13 miles outside of Joliet — to gather additional information Wednesday in hopes of determining whether a tornado touched down. Meanwhile, crews with Commonwealth Edison were working to restore power to the portion of 54,324 customers who experienced an outage. As of 8:30 a.m., the utility had restored power to 95% of those customers, a representative said.
The storm also dropped the largest recorded hail so far this year, even though hail is more commonly associated with spring storms, according to the weather service. Baseball-sized hail was reported in Earlville, a community north of Ottawa, off Interstate Highway 88 and about 80 miles from Chicago.
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“Some of the hail in Lee and LaSalle counties was as large as 2 inches in diameter. The hail in Earlville covered the ground and lasted for multiple hours before melting,” according to the weather service website.
Most areas in northern Illinois that had rain Tuesday received less than an inch, but two rain gauges near Deerfield recorded 1.5 inches and 1.02 inches. The storms also produced significant wind damage in Gibson City in Ford County, as well as the Minooka and Channahon area.
“Swathes of wind damage to mainly utility poles, trees, and trees on structures occurred, in particular from Morris to Minooka to Channahon to Manhattan across Grundy to Will counties,” the weather service said.
Minooka Central Community High School’s main campus building “endured damage caused by the extreme weather,” according to a letter from District 111 administrators to parents.
“Out of an abundance of caution, and until MCHS Administration can fully assess the damage, certain classes will be moved to alternate locations for a full day of learning (Wednesday),” said the letter, signed by Principal Bryan Zwemke.
Zwemke said there had been “reports of downed power lines, uprooted trees, and other debris in the streets throughout the area” and warned community members against driving or leaving their shelters Tuesday night.
“Adversity does not build character, it reveals it. Today our students and staff showed patience, resolve, and selfless duty to one another,” he said.
About 1 p.m. Tuesday, the weather service also reported 1.5-inch hail in Harvard, a far northwest suburban community in McHenry County near the Wisconsin border. In Bull Valley, also in McHenry County, a trained weather spotter recorded a 68 mph wind gust, the weather service said.
Following the storm, which also brought a cold front to the area, temperatures remained cool Wednesday. But forecasters said warmer weather should prevail by the weekend. Mostly sunny skies were expected Thursday and Friday, but the high temperature isn’t expected to exceed 80 degrees.
By Saturday, the daytime high temperature should jump about 10 degrees to a high of 90 degrees, according to the weather service. For more forecast information, visit the Tribune’s weather page.
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