Dangerous heat and humidity will continue across much of Iowa through Saturday, September 5, with the National Weather Service expanding heat alerts into additional portions of the state Friday morning.
Much of Iowa is now under a Heat Advisory, while portions of eastern and southeast Iowa are under a more serious Extreme Heat Warning. Heat index values of 100 to 110 degrees will be possible in the hottest areas.
The prolonged nature of the heat is also a concern. Warm overnight temperatures will provide limited relief before dangerous heat and humidity return during the afternoon.
Heat Advisory
A Heat Advisory covers a large portion of Iowa. The National Weather Service in Des Moines expanded the advisory northward Friday morning to include Sac, Calhoun, Webster, Hamilton, Hardin, Grundy and Black Hawk counties. This includes communities such as Fort Dodge, Webster City, Iowa Falls, Grundy Center, Cedar Falls and Waterloo. Heat index values in these areas could reach around 105 degrees.
The advisory also includes areas such as Ames, Boone, Carroll, Denison and Marshalltown, where heat index values could similarly climb to around 105 degrees.
Across central and southern Iowa, the Heat Advisory includes the Des Moines metro, Newton, Grinnell, Pella, Indianola, Ottumwa, Creston, Atlantic, Osceola and Centerville, among many other communities. The advisory in these areas remains in effect through 7 p.m. Saturday.
Southwest Iowa will also experience potentially dangerous conditions through Saturday evening. Afternoon heat index values could reach 108 degrees, while overnight temperatures may only fall into the 72 to 78 degree range. The advisory includes communities such as Council Bluffs, Harlan, Red Oak, Glenwood, Shenandoah and Clarinda.
Additional Heat Advisories are in effect Friday across portions of northwest, west-central and northeast Iowa, including the Sioux City, Storm Lake, Cherokee, Oelwein and Elkader areas. Some of these advisories are currently scheduled to expire Friday evening rather than Saturday.
The duration of this heat is particularly important. The National Weather Service notes that heat index values may not reach 105 degrees everywhere each day, but the combination of several days of heat and limited overnight relief has prompted the multi-day Heat Advisory.
Extreme Heat Warning
An Extreme Heat Warning is in effect across portions of east-central and southeast Iowa through 7 p.m. Saturday.
The warning includes areas such as Iowa City, Davenport, Bettendorf, Muscatine, Burlington, Washington, Fairfield, Mount Pleasant, Fort Madison and Keosauqua.
Heat index values across the warned area are expected to reach 100 to 110 degrees. These conditions can significantly increase the risk of heat-related illness, especially for people spending extended periods outdoors.
The Extreme Heat Warning represents the more serious of the two heat alerts currently affecting Iowa. Residents in the warned area should take extra precautions to avoid prolonged exposure to the heat and humidity.
Why the Prolonged Heat Is a Concern
While the highest heat index values will occur during the afternoon, this heat wave isn’t just about a few exceptionally hot hours.
Warm nighttime temperatures mean some areas will experience little relief from the heat overnight. That becomes increasingly important when dangerous heat lasts for several consecutive days.
People without adequate air conditioning can experience accumulating heat stress when homes and buildings remain warm overnight before temperatures quickly climb again the following day.
Staying Safe During the Heat
Anyone spending time outside Friday or Saturday should take the heat seriously. Drink plenty of water, spend as much time as possible in air-conditioned locations, wear lightweight and loose-fitting clothing, and move strenuous outdoor activities to the early morning or evening when possible.
Check on older adults, neighbors and others who may be particularly vulnerable to prolonged heat. Children and pets should never be left inside an unattended vehicle, even briefly, because interior temperatures can quickly become deadly.
Outdoor workers should take frequent breaks in shaded or air-conditioned areas. Anyone showing signs of heat stroke—including confusion, loss of consciousness or an extremely high body temperature—needs immediate emergency medical attention.
Stay with IowaWeather.com and the Iowa Storm Chasing Network for the latest Iowa weather updates throughout the weekend.