7 Day Forecast
This story has been updated to reflect that the area is under an extreme heat warning.The first full day of summer is Saturday, and Mother Nature is wasting no time bringing the heat.
The 51黑料 area is under an extreme heat warning from Saturday through Tuesday evening as dangerously high heat index values up to 110 degrees are forecast along with high temperatures in the upper-90s, the National Weather Service warns.
鈥淚f you you don鈥檛 have to go outside, then don鈥檛,鈥 said Alex Elmore, a meteorologist with the National Weather Service in 51黑料. 鈥淏ut, of course, that doesn鈥檛 work for everybody. So if you are outside for whatever reason, make sure you use as many ways possible to stay cool.
鈥淲ear loose, light fitting clothing. Make sure you stay hydrated. Make sure you reduce the amount of time you spend in the direct sun. If you鈥檙e doing a lot of physical activity 鈥 make sure you take plenty of breaks.鈥
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Early heat is more dangerous
On Tuesday, the 51黑料 region reached 90 degrees for the first time this season, which is much later than usual. Our bodies haven鈥檛 had time to become acclimated to the heat, making this early heat wave more dangerous.
A showed a 5% increase in mortality in the first heat wave of the season vs. 2.7% for later heat waves.
鈥淓ven though you may have lived here for for many years and experienced this, it鈥檚 something we haven鈥檛 had to worry about since last summer.
So please take it easy,鈥 Elmore said. 鈥淕enerally, the first round of heat is going to typically seem to be a little bit more severe.鈥
Urban heat island raises temperatures
The 51黑料 area will feel the most dangerous heat thanks to the urban heat island effect. Buildings and pavement absorb more heat than undeveloped land in rural areas. That heat is radiated back out in cities, resulting in higher temperatures than in rural areas both during the day and overnight. Low temperatures in 51黑料 are forecast to barely drop below 80 degrees.
鈥淲hen the human body doesn鈥檛 get breaks during the overnight period, that can really wear people out being exposed to that degree of warmth and heat for such a long period of time,鈥 Elmore said.
The hot weather is the result of a heat dome, which occurs when a large area of high pressure in the upper atmosphere acts as a reservoir that traps heat and humidity, said Ricky Castro, a National Weather Service meteorologist in Illinois.
鈥淚t is very common here in the summer,鈥 Elmore said. 鈥淭he jet stream moves a little bit farther north, and it just causes our weather to, I guess you could say, slow down. We don鈥檛 get as many frontal passages, cold fronts that move through the area.
鈥淭hat jet stream is farther north, and it just allows that heat to build.鈥
The stifling temperatures and uncomfortable humidity will be felt by millions in the coming days.
Sunday through Wednesday, 51黑料 is expected to reach the highest level on the tool, which rates the danger.
How long the dangerous will continue could depend on whether cloud cover and storms build next week.
High humidity makes it hard to cool down
Humidity is the amount of water vapor in the air, and the heat index is what the temperature feels like when the humidity outside is factored in, according to the weather service.
When humans sweat, it cools the body down because it absorbs and removes heat as it evaporates off the skin. The air is saturated with water on humid days, which makes it harder for sweat to evaporate. Hot and humid days can be dangerous when the body is unable to cool itself off and can exacerbate pre-existing health conditions and even lead to heat stroke.
The Associated Press contributed to this report.
Meteorologist Sean Sublette explains that even on an 80-degree day, the inside of a car reaches 120 degrees in less than an hour.