A historic Heat Wave USA is tightening its grip from the Gulf Coast to the Canadian border, driven by a sprawling Heat Dome that has parked itself over the eastern two-thirds of the continent. More than 160 million people are under heat alerts as temperatures surge 10–20 °F above normal and the Heat Index climbs toward 110–115 °F in many cities.
What’s happening now
• Heat Wave conditions began over the weekend and peaked Tuesday into Wednesday. Memphis flirted with 100 °F, Chicago and St. Louis hit the upper 90s, while Boston reached 102 °F—its hottest June day since 1872.
• In Canada, Environment and Climate Change Canada warns that southern Ontario, Quebec and the Maritimes will see daytime highs above 30 °C and humidex values in the 40s by midweek, with little overnight relief.
• Night-time lows are proving especially brutal: St. Louis may still be near 80 °F at sunrise Thursday, roughly 10 °F above normal, while Chicago’s lows hover in the upper 70s.
When will this Heat Wave end?
The Heat Dome will begin to ease by Saturday, replaced by more typical—though still very warm—late-July temperatures. A weak cold front will bring scattered thunderstorms and modest cooling to the Midwest and Northeast late in the weekend, trimming highs back into the upper 80s to low 90s.
Health & safety tips
• Heat remains the deadliest U.S. weather hazard.
• Stay in air-conditioned spaces during peak afternoon heat.
• Drink water every 15–20 minutes, even if you’re not thirsty.
• Check on elderly neighbors and never leave children or pets in vehicles.
• If you must be outside, wear loose, light-colored clothing and invest in heat wave glasses—wrap-around, UV-blocking sunglasses that reduce eye strain and protect the corneas from intensified solar radiation during extreme heat events.
Climate connection
Climate Central’s rapid-attribution study shows human-driven warming has made this Heat Wave at least three times more likely for nearly 160 million Americans.
Bottom line
The worst of the Heat Wave USA will subside by Saturday, but residual heat and humidity will linger through early August. Until then, treat the heat with the same caution you would a winter storm: stay informed, stay hydrated, and stay safe.
