Joliet temperature hits 99; missed first three-digit mark since 2012

Joliet — Temperatures grazed the century mark in the Chicago region Tuesday, and reached 99 in Joliet.

Temps were just shy of the record set back in 1988, when temperatures reached 101 degrees, National Weather Service meteorologist Kevin Doom said.

The last time temperatures reached 100 degrees at O’Hare International Airport, which marks the official location for Chicago’s weather data, was back in July 2012, weather service data shows. On July 5 and 6, 2012, temperatures peaked at 103 degrees.

On Tuesday, temperatures peaked between 2 and 4 p.m., Doom said. Joliet hit 99 at 4 p.m.

While the heat index, also called the “feels-like” temperature, did reach north of 100 degrees last week, the weather service focuses on the actual temperature, Doom said.

The heat index this time around also won’t be as high, as humidity is much lower than it was last week, Doom said.

The dew-point temperature, which helps measure how much water is in the air, is projected to be in the 60s. Last week, that marker was in the 70s, driving the feels-like up to between 105 and 110, Doom said.

“That’s what really drives up the heat index is how much water is in the air,” he said. “Our body cools down by sweating and that sweat evaporating from our body. But when the air is humid, it doesn’t evaporate effectively … and almost acts as an insulator for the heat.”

At Midway International Airport in Chicago last week, 100-degree weather was recorded on both June 14 and 15, according to data from the weather service.

Despite the heat Tuesday, forecasts have temperatures dipping back to the 80s Wednesday and Thursday, with temperatures near Lake Michigan possibly in the 70s on Thursday, Doom said.

Friday could be a similar story, according to forecasts from the weather service. Saturday could see its high get into the lower 90s before Sunday and Monday see a cool down with temperatures expected to be in the mid-70s.