Excessive Heat — Sully, South Dakota

2023-08-21 to 2023-08-23 · Sully, South Dakota

Wider weather episode

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.

Source: NOAA Storm Events Database, event_id 1111353. Narrative written by the NWS forecast office that issued the report.