A large ridge of high pressure aloft set up over the center of the country around August 20th, leading to a week-long heatwave across southern Illinois. High temperatures were primarily only in the low to mid 90s most days, but the main headline was the extreme humidity levels witnessed over the entirety of this event. Portions of the region experienced very heavy rainfall amounts of 15 to 25 inches from July 1st through mid August. This set the stage for record levels of evapotranspiration from the vegetation and crops. Dew points, a measure of humidity levels, were routinely in the upper 70's to lower 80's, with several locations peaking in the mid 80's. Carbondale reached its highest dew point of 82 degrees on the 25th. This caused heat index readings to peak between 105 and 120 degrees each day from August 20th through the 25th. The high humidity levels also led to dense fog formation several nights during this event, which was rather unusual for a prolonged heat wave. The highest hourly heat index readings at Carbondale were 111 on the 20th, 117 on the 21st, 111 on the 22nd, 108 on the 23rd, 110 on the 24th, and 114 on the 25th. Many schools cancelled outdoor activities or moved them indoors, including football practices.

Excessive Heat in HARDIN, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in JEFFERSON, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in POPE, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in JOHNSON, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in MASSAC, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in FRANKLIN, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in WILLIAMSON, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in PERRY, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in EDWARDS, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in JACKSON, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in PULASKI, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in SALINE, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in WABASH, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in WAYNE, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in UNION, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in GALLATIN, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in WHITE, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in ALEXANDER, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in HAMILTON, ILLINOIS
From 20-AUG-23 11:00:00 to 25-AUG-23 17:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS