A heat dome to the south resulted in temperatures topping out in the 90s to just over 100 degrees, with dewpoints in the 70s to low 80s, generating heat index values in excess of 100 degrees for a three day period. During this timeframe, most weather stations reported heat index values falling below 75 degrees for at least a few hours in the morning, however.
During the afternoon on Monday, moisture pooling along a weak warm front resulted in the highest heat index values across central South Dakota. The Remote Automatic Weather Station (RAWS) in southeast Hand County reported a peak heat index of 118 degrees, while Pierre Regional Airport registered a peak heat index of 116 in the afternoon.
Heat index values again topped above 100 degrees for much of central and northeast South Dakota on Tuesday as that weak warm front shifted northeast slightly. The highest heat index values were focused across Grant and southern Roberts counties, with a total of 20 different weather stations recording a heat index between 111 and 136 degrees in Grant County alone. The Automated Weather Observing System (AWOS) 3 miles northeast of Milbank recorded a temperature of 93 and a dewpoint of 86, resulting in a heat index of 125, and while nearby stations were higher, we do not know the citing details of these individual stations.
The heat and humidity eased slightly for Wednesday with a broader coverage of 100 to 112 degree heat index values. Even north central South Dakota, which had seen cloud cover during the two days prior, witnessed heat index values above 105 degrees. This period of excessive heat wasn't alleviated until a cold front moved through Wednesday night.

Excessive Heat in BUFFALO, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in HUGHES, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Excessive Heat in SPINK, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in LYMAN, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in SULLY, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in CODINGTON, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Excessive Heat in POTTER, SOUTH DAKOTA
From 22-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in CLARK, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in WALWORTH, SOUTH DAKOTA
From 23-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in JONES, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in HYDE, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in GRANT, SOUTH DAKOTA
From 22-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Excessive Heat in FAULK, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in DAY, SOUTH DAKOTA
From 22-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in HAMLIN, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in HAND, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

Excessive Heat in STANLEY, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in BROWN, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Excessive Heat in CORSON, SOUTH DAKOTA
From 23-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in EDMUNDS, SOUTH DAKOTA
From 22-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in DEUEL, SOUTH DAKOTA
From 21-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in MARSHALL, SOUTH DAKOTA
From 22-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in DEWEY, SOUTH DAKOTA
From 23-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in MCPHERSON, SOUTH DAKOTA
From 22-AUG-23 12:00:00 to 23-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Excessive Heat in ROBERTS, SOUTH DAKOTA
From 22-AUG-23 12:00:00 to 22-AUG-23 20:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet