The National Weather Service office in the Quad Cities reported that all major observation sites in its service area hit a heat index of at least 110 degrees during the two-day extreme heat event on July 26 and 27.
The highest peak heat index reading was 128 in Macomb.
Elsewhere, Fort Madison reached 125, and the heat index was as high as 121 in Keokuk and Burlington.
The maximum temperature reached during the two-day period was 100 degrees in Keokuk. Temperatures reached 96 in Fort Madison and 94 in Burlington and Macomb.
A heat dome and high dew points combined to create the extreme conditions.
The NWS said there was a 10-hour stretch of dew points above 80 at the Quad Cities International Airport on July 26. The agency said this was the most consecutive hours of that high of a dew point since official observations began at the airport in 1932.
The airport also observed its highest hourly dew point (82°) since 1999.
