While parts of the 2023 summer had warm to hot temperatures, it took until middle to late August for the combination of hot temperatures and higher humidity levels to build a heat wave. Excessive heat advisories and warnings were initially issued on Monday, August 21st for select counties, expanding for all counties in northeast Iowa until Thursday, August 24th. Heat indices reached and exceeded 100 degrees each day, with overall highest heat indices occurring on Wednesday, August 23rd. During this time, maximum daytime heat indices reached 119 degrees at Decorah (Winneshiek County) and 118 degrees at Charles City (Floyd County) and Oelwein (Fayette County). Many sites in northeast Iowa recorded heat indices of 110 to 120 degrees over the four days from August 21st to August 24th.

Excessive Heat in FLOYD, IOWA
From 21-AUG-23 11:00:00 to 24-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

The combination of anomalously high temperatures and humidity resulted in maximum heat indices of 116 degrees on Tuesday, August 22nd and 118 degrees on Wednesday, August 23rd at the automated weather observation station in Charles City.

Excessive Heat in CHICKASAW, IOWA
From 22-AUG-23 11:00:00 to 22-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

The combination of anomalously high temperatures and humidity resulted in maximum heat indices of 108 degrees on Tuesday, August 22nd and 118 degrees on Wednesday, August 23rd in New Hampton.

Excessive Heat in FAYETTE, IOWA
From 22-AUG-23 11:00:00 to 24-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

The combination of anomalously high temperatures and humidity on Tuesday, August 22nd and Wednesday, August 23rd resulted in maximum heat indices of 106 to 118 degrees in parts of Fayette County. The maximum heat index reached 108 degrees on Tuesday and 118 degrees on Wednesday at the automated weather observation station in Oelwein.

Excessive Heat in ALLAMAKEE, IOWA
From 22-AUG-23 11:00:00 to 24-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

The combination of anomalously high temperatures and humidity on Tuesday, August 22nd and Wednesday, August 23rd resulted in maximum heat indices of 103 to 108 degrees in parts of Allamakee County.

Excessive Heat in CLAYTON, IOWA
From 22-AUG-23 11:00:00 to 24-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

The combination of anomalously high temperatures and humidity on Tuesday, August 22nd and Wednesday, August 23rd resulted in maximum heat indices of 102 to 113 degrees in parts of Clayton County. The maximum heat index reached 106 degrees on Tuesday in Mcgregor and 113 degrees on Wednesday in Monona.

Excessive Heat in WINNESHIEK, IOWA
From 22-AUG-23 11:00:00 to 24-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

The combination of anomalously high temperatures and humidity on Tuesday, August 22nd and Wednesday, August 23rd resulted in maximum heat indices of 108 to 119 degrees across Winneshiek County. The maximum heat index reached 109 degrees on Tuesday near Jackson Junction and 119 degrees on Wednesday at the automated weather observation station in Decorah.

Excessive Heat in MITCHELL, IOWA
From 21-AUG-23 11:00:00 to 24-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

The combination of anomalously high temperatures and humidity resulted in maximum heat indices of 114 degrees on Tuesday, August 22nd and 115 degrees on Wednesday, August 23rd at the automated weather observation station in Stacyville.

Excessive Heat in HOWARD, IOWA
From 22-AUG-23 11:00:00 to 24-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

The combination of anomalously high temperatures and humidity resulted in maximum heat indices reaching 112 degrees on Tuesday, August 22nd in Saratoga and 116 degrees on Wednesday, August 23rd in Riceville.