A prolonged stretch of hot and humid weather will continue across much of Iowa through Thursday, with the National Weather Service expanding and extending Heat Advisories across a large portion of the state.
Heat index values could reach 100° to 105° during the afternoon hours, creating potentially dangerous conditions for anyone spending extended periods outdoors. The combination of several consecutive hot days and warm overnight temperatures will also increase the risk of heat-related illness.
Heat Advisory Expanded Across Iowa
As of Tuesday afternoon, September 1, Heat Advisories cover much of central, southern, eastern and southwest Iowa.
Across central, south-central and southeast Iowa, including the Des Moines metro, the Heat Advisory has been extended until 7 p.m. Thursday. Heat index values could reach approximately 103° during the hottest portions of the day.
The advisory includes communities such as Des Moines, Waukee, Perry, Adel, Newton, Grinnell, Winterset, Indianola, Pella, Oskaloosa, Creston, Osceola, Ottumwa, Centerville and Bloomfield.
Farther west, additional portions of southwest Iowa will enter a Heat Advisory at 1 p.m. Wednesday, continuing through 7 p.m. Thursday. This includes Council Bluffs, Glenwood, Red Oak, Shenandoah and Clarinda. Heat index values there could climb as high as 105°.
Eastern Iowa Could Feel as Hot as 105°
The heat will not be limited to southern Iowa. The National Weather Service in the Quad Cities has expanded its Heat Advisory northward to include additional portions of eastern and northeast Iowa, including Cedar Rapids, Dubuque, Independence, Manchester, Vinton, Anamosa and Maquoketa. The advisory remains in effect through 7 p.m. Thursday, with heat index values potentially reaching 105°.
Areas farther south and east, including Iowa City, Davenport, Bettendorf, Muscatine, Burlington, Washington, Fairfield and Fort Madison, are also under the Heat Advisory through Thursday evening.
The National Weather Service Quad Cities says hot and humid conditions will persist through Thursday, with afternoon heat indices generally reaching the mid-90s to around 105°. Warm nighttime temperatures will provide limited relief and add to the overall heat stress.
Why This Heat Can Become Dangerous
The concern isn’t simply how hot it gets during one afternoon. Several consecutive days of heat and humidity can gradually take a toll on the body, especially when temperatures remain warm overnight. Southwest Iowa could see overnight lows between 75° and 80°, offering relatively little opportunity to recover from daytime heat.
This cumulative heat stress can be particularly dangerous for people working outside, athletes, older adults, young children and those without reliable access to air conditioning.
Even where the actual air temperature remains in the 90s, high humidity makes it more difficult for sweat to evaporate efficiently. That reduces the body’s ability to cool itself and causes the apparent temperature—or heat index—to climb above the actual temperature.
How Hot Will It Feel in Iowa?
For many locations within the advisory, afternoon heat indices will reach the upper 90s to lower 100s, with localized readings around 103° to 105° possible.
Conditions observed Tuesday afternoon already showed how quickly apparent temperatures were climbing. At 2:54 p.m., Des Moines International Airport reported an air temperature of 95° with a heat index of 100°.
The hottest conditions will generally affect central, southern, southwest and eastern Iowa, while northern Iowa will have a somewhat different weather concern as thunderstorms move through portions of the region.
Staying Safe During the Iowa Heat
Anyone spending time outdoors Wednesday or Thursday should take the heat seriously.
Drink plenty of water throughout the day, even before you become thirsty. Whenever possible, spend time in air conditioning and avoid prolonged exposure to direct sunlight.
Outdoor work, exercise and other strenuous activities should be moved to the morning or evening when temperatures are lower. Lightweight, loose-fitting clothing can also help the body stay cooler.
Workers who must remain outside should take frequent breaks in shaded or air-conditioned areas. The National Weather Service also recommends checking on relatives and neighbors who may be especially vulnerable to the heat.
Never leave children or pets inside a parked vehicle, even for a short period.
When Will the Heat End?
For most of the Iowa counties currently under an advisory, the Heat Advisory is scheduled to expire at 7 p.m. Thursday, September 3.
That does not necessarily mean the hot weather will immediately disappear.
The overall weather pattern remains supportive of above-normal heat and humidity late in the week, and additional extensions or expansions of heat-related alerts may be needed if the prolonged heat continues. The National Weather Service Omaha specifically notes that its Heat Advisory could be extended or expanded depending on how the heat wave evolves.
Thunderstorms may also complicate the temperature forecast at times by temporarily cooling some locations while leaving others hot and humid.
For now, Iowans should prepare for at least two more afternoons of potentially dangerous heat Wednesday and Thursday, especially across the southern two-thirds and eastern portions of the state.
Continue checking IowaWeather.com and the ISCN Weather app for the latest forecast information, Heat Advisory updates and any changes to the expected duration of the heat.