CHICAGO — Very dangerous, life-threatening atmospheric conditions will exist through Monday across the Chicago area.
With daytime temperatures expected to warm into the middle and upper 90s, along with high humidity and abundant sunshine and nighttime readings dropping not much lower than 80 degrees, an Excessive Heat Warning (purple-shaded area on the highlighted map) has been issued for Chicago and Cook County until Monday evening. A Heat Advisory (orange-shaded area on the highlighted map) has been issued until early Monday for Chicago-area counties in northeast Illinois into northwest Indiana where similar daytime conditions are expected, but nighttime temperatures may fall into the middle 70s.
The Heat Index should exceed 100 degrees in many parts of the area each day, likely peaking above 105 degrees Sunday afternoon. The upcoming Summer Solstice occurs next Thursday, meaning the afternoon sun is reaching the highest point in the sky with the most intense rays – sufficient to raise the apparent heat index another 5 to 15-degrees, depending upon how long you stay out in the sunlight. A break in the heat cannot be expected at night with overnight readings staying in the 90s many areas before midnight and dropping only into the 80s after that until warming resumes the following morning. This failure to have a recuperative break in the heat/humidity was considered one of the primary causal factors in the heat deaths incurred in the 1995 Chicago heat disaster.
Stay in the shade or air conditioning as much as possible, drink plenty of water and look in on those considered most susceptible to heat injury.
The Air Quality Alert in effect until early Monday for several northwest Indiana Counties, including Lake and Porter Counties, warning of high ozone levels will combine with the heat and humidity to create hazardous conditions especially for those with respiratory problems.
Note on map below the extensive coverage of the Heat Warnings/Advisories across the Midwest and Upper/Mid-Mississippi Valley area. Excessive Heat Warnings are in effect for Minneapolis and St. Louis in addition to Chicago.