The heat wave smothering the Midwest and much of the central U.S. peaks Monday and Tuesday, holds through Wednesday, and finally breaks Thursday into Friday as a cold front slides down from Canada, according to National Weather Service forecasts. For Minneapolis and the Upper Midwest, near-normal highs in the mid-to-upper 80s return by the weekend, while the South and parts of the West stay hot longer. Until then, forecasters say the biggest danger isn't the afternoon peak — it's the nights: the NWS projects more than 90 temperature records will be tied or broken through Wednesday, and most of them are overnight heat records.
Which States and Cities Are Under Heat Alerts Right Now?
The core of this heat dome is parked over the Upper Midwest and northern Plains. An extreme heat warning covers the Twin Cities, where the NWS expects highs in the mid-90s and heat index values from 100 to as high as 107. Heat advisories blanket much of Wisconsin — NWS forecasts put the heat index near 103 in Green Bay and 100 in Appleton — while Chicago's heat index is forecast to reach about 104. Across the northern Plains and Midwest, record highs of 95 to 105 are forecast through midweek.
The heat isn't confined to the middle of the country. NWS offices issued extreme heat warnings for inland Southern California (into Thursday) and parts of southeastern Idaho, while along the Gulf Coast and Southeast, Miami, Tampa, Charleston and Galveston aren't expected to drop below 80°F even at night, per AP reporting on the NWS outlook. It's the same setup that baked the mid-Atlantic earlier this summer — see our DC heat wave coverage.
Day-by-Day: When Does the Heat Wave Break?
- Monday–Tuesday, July 13–14: The peak. The heat dome maxes out over the Upper Midwest, with heat index values of 100–107 from the Twin Cities to Chicago and record highs across the northern Plains. Overnight lows only fall to the mid-70s.
- Wednesday, July 15: Still dangerous. Most of the 90-plus records the NWS is tracking fall by Wednesday. Milwaukee-area advisories run through Wednesday evening as a weak cold front begins sagging south out of Canada.
- Thursday, July 16: The turn. The Twin Cities extreme heat warning runs through 9 p.m. Thursday, with scattered storms firing along the front and starting to knock temperatures down from north to south.
- Friday, July 17: Relief spreads across the Upper Midwest and Great Lakes as cooler, drier Canadian air filters in behind the front.
- Weekend, July 18–19: Minneapolis returns to the mid-to-upper 80s — close to seasonal norms — while the South and Gulf Coast hold onto the heat and steamy 80-degree nights.
Why Record Warm Nights Are the Real Danger
Health experts say overnight temperatures that fail to cool down are even more dangerous than soaring daytime highs. Your body sheds heat stress at night; when the low only reaches the mid-70s or warmer, that recovery never happens and the strain compounds. Cities built for frigid winters — Fargo, North Dakota and International Falls, Minnesota, of all places — are forecast to stay above 70°F overnight this week.
University of Georgia meteorology professor Marshall Shepherd told the AP that's "where the health outcomes are amplified, particularly for the elderly and vulnerable communities." University of Washington public health scientist Kristie Ebi adds that heat-wave "mortality starts the second or third day" — exactly the stretch the Midwest is entering now.
What Is a Heat Index? (Plain-Language Explainer)
The heat index is the "feels-like" temperature: air temperature plus humidity, converted into what your body actually experiences. Your body cools itself by evaporating sweat — but humid air slows that evaporation, so the same 90°F day feels far hotter when the air is muggy.
A quick example from the NWS chart: 90°F with 70% humidity feels like about 105°F. And the heat index is measured in the shade — the NWS notes direct sunshine can add up to 15 degrees on top of it. That's why a "96-degree day" in Minnesota this week can genuinely feel like 107.
How to Stay Safe Until the Cooldown
- Hydrate constantly — don't wait until you're thirsty; skip alcohol during peak heat.
- Get to air conditioning for part of the day; many cities open free cooling centers. Fans alone aren't enough above the mid-90s.
- Shift outdoor work and exercise to early morning, with shaded breaks.
- Check on elderly neighbors daily — they're the most common victims of warm-night heat stress.
- Never leave children or pets in a car, even for minutes.
- Know the signs: heavy sweating, dizziness and nausea mean heat exhaustion — cool down fast. Confusion, a racing pulse or hot dry skin means possible heat stroke: call 911.
Is This Connected to a Bigger Pattern?
This is already the second major heat dome of July 2026, arriving barely a week after the July Fourth event. Scientists caution that no single heat wave can be pinned on one cause, but forecasters have noted this summer is running hot against a backdrop of a strengthening El Niño — a pattern that historically loads the dice toward more extreme heat episodes. For what that could mean for the rest of 2026, read our Super El Niño explainer.
Frequently Asked Questions (FAQ)
How long will the heat wave last?
The heat peaks Monday–Tuesday, holds through Wednesday, and breaks Thursday into Friday as a Canadian cold front arrives. The Twin Cities are back to near-normal mid-to-upper 80s by the weekend; the South stays hot longer.
What is a heat index?
It's the "feels-like" temperature: air temperature combined with humidity. Humid air slows sweat evaporation — your body's cooling system — so 90°F with 70% humidity feels like about 105°F on the NWS chart.
Why are warm nights dangerous?
When overnight lows stay in the mid-70s or higher, the body never recovers from daytime heat stress. Researchers say heat-wave mortality typically starts climbing on the second or third day — the elderly and people without air conditioning are most at risk.
What states are under heat advisories?
Alerts stretch from the northern Plains through the Midwest into the West and South — including Minnesota (extreme heat warning in the Twin Cities), Wisconsin, Illinois, North Dakota, inland Southern California and southeastern Idaho. Check weather.gov for your exact location.
