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Expanding heat dome may reach Eastern Iowa this week
Or the region could get overnight thunderstorms on the edge of the dome
Jul. 23, 2023 5:00 am, Updated: Jul. 26, 2023 9:49 am
Eastern Iowa may find itself teetering between two weather possibilities this week: trapped in a dry, expanding heat dome, or shrouded in overnight thunderstorms on the dome’s outskirts.
A heat dome is a very hot air mass that forms when high-pressure conditions in the atmosphere trap warm air from rising, creating a cap. One has plagued much of the U.S. — from the Southwest into Texas — since early June. This week, it’s projected to spread farther north and east as jet streams shift north.
Increasing temperatures next week will result in very hot conditions for the second half of the week. The CPC has a slight-moderate risk of excessive heat late next week for us. The probability is increasing that heat index readings will exceed 100 degrees. #iawx #ilwx #mowx pic.twitter.com/Zu7YDq7Au9
— NWS Quad Cities (@NWSQuadCities) July 21, 2023
Projections are placing Eastern Iowa on the northeastern edge of that heat dome expansion. Meteorologists from the National Weather Service’s Quad Cities Bureau estimated the region has a 20 to 40 percent chance of getting enveloped by dome.
Regardless of its spot in the dome, Eastern Iowa will very likely start seeing temperatures surpassing 90 degrees by Tuesday. The area may see temperatures in the mid-90s Wednesday, Thursday and Friday. It will likely bring the hottest days of the summer so far.
“The question then becomes whether or not we hit the magic triple-digit” air temperatures, said NWS Quad Cities bureau meteorologist Brian Pierce.
Heat watches, warnings and advisories
Excessively hot conditions may prompt the National Weather Service to issue safety announcements to the public. These are based off ambient air temperatures and/or heat index values, which are “feels like” temperatures based on temperature and humidity.
The announcements include:
• Heat Advisory: means that temperatures of at least 100 degrees or heat index values of at least 105 degrees are expected generally within the next 24 hours.
• Excessive Heat Watch: means that heat index values are expected to reach or exceed 110 degrees and not fall below 75 degrees for at least a 48-hour period, beginning in the next 12 to 48 hours.
• Excessive Heat Warning: means that heat index values are expected to reach or exceed 110 degrees and not fall below 75 degrees for at least a 48-hour period, beginning in the next 24 hours.
If Eastern Iowa remains on the dome’s outskirts, it's in for a wetter week. Thunderstorms may roll through the area in the night, potentially bringing several rounds of heavy rain. Thursday and Friday night show decent chances of some precipitation.
It will likely grow warm in the daytime, but temperatures may not get as hot as they would under the full force of the heat dome. Still, any rain would make the area more humid, which would raise heat index values or “feels like” temperatures.
“We're either going to be in the heat dome and be high and dry, or if we're right on the edge, we could be quite wet. Right now, the models are offering very differing opinions on what could happen,” Pierce said.
The models should have clearer projects early this week.
How to keep yourself safe
If the NWS issues a heat advisory, watch or warning, both Linn and Johnson counties will have heat relief facilities available for residents.
Once heat levels hit a certain threshold, Johnson County compiles a list of accessible cooling centers per city and pushes it out to residents. The list typically includes locations like malls, swimming pools, community centers and libraries. Hours may be extended at those locations.
Johnson County tries to widely publish these resources one to two days before hot temperatures, said county emergency management coordinator Dave Wilson.
Linn County posts its heat relief locations, and other heat-related information, on its website: https://www.linncountyiowa.gov/707/Heat-Relief.
If hot temperatures plague Eastern Iowa, Linn and Johnson County emergency management coordinators have this advice for residents:
- Check on family and friends, especially older adults and at-risk individuals.
- Don’t leave children or pets in cars.
- Avoid drinking caffeine and alcohol, and stay hydrated. Keep your pets and livestock hydrated, too.
- Limit your time outdoors, particularly during midday when temperatures tend to be hottest. When outdoors, be sure to take breaks and wear protective clothing like hats and light-colored loose clothing. Apply sunscreen.
Even with the projected hot temperatures, RAGBRAI — the cross-state bike ride still is scheduled as planned, said Nick Pfeiffer, Coralville’s vice president of public affairs and its RAGBRAI publicity chair. It’s the sixth time Coralville has hosted an overnight stop on the race’s trail.
The city is proactively prepping for the incoming 40,000-plus riders and the heat. It’s stocking up on ice and first responders, setting up emergency shelters, and training volunteers for emergency actions. Coralville is also offering free movies inside the Coralville Center for the Performing Arts so riders can have an air-conditioned reprieve from the heat.
“We're gonna be as ready as any town there is,” Pfeiffer said. “The heat may actually deter some of those people from riding for the day if they don't want to enter that type of climate.”
Brittney J. Miller is the Energy & Environment Reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.
Comments: (319) 398-8370; brittney.miller@thegazette.com
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