Chicago Weather

Chicago heat timeline: It could soon feel like 115 degrees. Here's when and for how long

"Dangerous" heat and humidity will build beginning Tuesday, the NBC 5 Storm Team said, but that's only the start

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It's about to get dangerously hot in the Chicago area, but when can you expect the highest temperatures and how hot will it get?

It depends on the metrics you're looking at.

Heat indices, or feels-like temperatures, could reach as high as 115 degrees for some.

The forecast has led to alerts for many counties, as the heat could mark some of the highest temperatures seen in the last decade.

So what can you expect and when? Here's a breakdown:

Tuesday: Heat Begins

"Dangerous" heat and humidity will build beginning Tuesday, the NBC 5 Storm Team said.

A heat advisory begins at 11 a.m. for DeKalb, Kane, LaSalle, Kendall, Grundy, Kankakee and Will counties.

During that time, "heat index values up to 105 degrees are expected," the alert said.

According to the NBC 5 Storm Team, temperatures on Tuesday are expected to reach the low 90s, with humidity making temperatures feel above 100 degrees inland.

With sweltering temperatures and heat indices over 110 degrees on the way, a heat advisory and an excessive heat watch will soon go into effect for the Chicago area, the National Weather Service said.

Wednesday: Hottest Heat Indices of the Week

Wednesday is when some of the hottest air of the year is expected to move in, NBC 5 Meteorologist Kevin Jeanes said.

The NWS has issued an excessive heat watch for Wednesday, for all of northeastern Illinois and northwestern Indiana. An "excessive heat watch" -- which means dangerous heat is possible -- will likely lead to excessive heat warnings and advisories in the coming days, Jeanes said.

Air temperatures Wednesday could reach into the upper-90s, with a forecast high of 97 degrees.

According to the NWS, Wednesday will see "dangerously hot and humid conditions with heat index values of 110 to 115 degrees possible."

"Extreme heat and humidity will significantly increase the potential for heat related illnesses, particular for those working in outdoor activities," the alert added.

According to forecast models, thunderstorms may develop over Lake Michigan Wednesday and Thursday, however, potentially disrupting the hot air mass.

Thursday: Even Warmer Air, But Less Humidity

With air temperatures as high as 99 degrees, Thursday looks to be even hotter than Wednesday, but with lower humidity expected, things may feel only slightly cooler than Wednesday.

Heat indices still look to remain well-above 100 degrees, however.

"When we talk about a feels like temperature, that is something that is calculated. You can't take a thermometer outside and do some things and figure out what the feels-like temperature is - that's a calculation," NBC 5 Storm Team Meteorologist Pete Sack said. "And part of that calculation is based on the amount of moisture that's in the atmosphere. And actually on Wednesday, there's going to be a little bit more moisture in the atmosphere than Thursday. So what that means is when there's more moisture in the atmosphere, when you sweat, the sweat on your body, when it gets evaporated off your body, it cools you off. When we have high dew points, high humidity values ... it makes it a lot more difficult for that sweat to evaporate off your skin and it makes it a lot more difficult for you to feel even cooler. So even though the temperature is going to be a degree or two warmer on Thursday, because the humidity values are going to be higher on Wednesday, the heat index values will likely be very similar both days."

Friday: Relief Arrives

The good news is the heat isn't expected to last long, as a cold front is expected to move in late Thursday night, bringing some relief by Friday.

High temperatures Friday are expected to sit in the 80s, dropping into the 70s by the weekend.

How Unusual is This Heat?

The temperatures Wednesday and Thursday aren't expected to be record-breaking, but they aren't exactly typical for the area.

According to Jeanes, Wednesday and Thursday could both be among the hottest days seen in Chicago in the last 10 years.

Wednesday and Thursday could be in the ‘top 3 hottest days in Chicago in the last 10 years,’ the NBC 5 Storm Team said

While the area did see a 98-degree day in June 2022, the last time such temperatures were recorded here was 2012.

"It's not terribly unusual, but it's kind of like the this is the opposite of the polar vortex," Sack said. "We typically see hot temperatures in the months of July and August especially, but this is more intense heat than we're used to when we see those temperatures, especially when it starts to climb over 95 for high temperatures and those heat index values go well into the triple digits. That's what we're looking at more extreme heat than we typically see."

Symptoms to Watch For

In anticipation of the heatwave, doctors are advising people to do anything they can to prevent heat-related illness, but also be aware of the signs and symptoms -- in the event that someone around them becomes ill.

The most serious heat-related illness, heat stroke, can cause permanent disability or death if not treated. According to the Centers for Disease Control and Prevention, heat stroke occurs when the body can no longer control its temperature. If heat stroke does occur, a person's body temperature can rise to 106 degrees or higher within 15 minutes.

The following are symptoms of heat stroke:

  • Confusion, altered mental status, slurred speech
  • Loss of consciousness (coma)
  • Hot, dry skin or profuse sweating
  • Seizures
  • Very high body temperature

If you think heat stroke is a possibility and you notice symptoms -- call 911 immediately.

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