After a slow start to summer across the northern U.S., a significant heat wave is anticipated as astronomical summer begins.

The FOX Forecast Center reports a strong ridge of high pressure will shift eastward, bringing scorching temperatures to cities such as Chicago, Detroit, and along the Interstate 95 corridor.

“Big ridges in summer typically indicate intense heat, and this one could be particularly noteworthy,” said FOX Weather meteorologist Stephen Morgan.

This heat event will peak from Sunday to Thursday, affecting hundreds of millions with temperatures that may be a few degrees above normal or up to 20 degrees higher.

While hitting 100°F may be rare for some areas, the combined effect of high temperatures and humidity will make it feel even hotter.

3

Heat indices—how hot it feels considering humidity—are predicted to reach triple digits in many locations.

Primarily affected areas include Chicago, Detroit, Pittsburgh, Philadelphia, New York City, and Washington D.C.

NYC rarely surpasses 100°F in June, with only three such days historically, while Philadelphia has experienced nearly a dozen such days, mostly in the 1990s.

3

The National Weather Service may issue heat advisories, watches, or warnings as conditions worsen, especially for vulnerable groups like children, the elderly, outdoor workers, and those without air conditioning.

3

To mitigate heat risks, authorities may open cooling centers and advise residents to stay hydrated and avoid peak heat hours.

As the ridge shifts east later in June and early July, temperatures are expected to moderate, with increased cloud cover and rainfall brought by frontal systems.

However, the hottest days of summer generally occur in mid to late July when solar radiation peaks, marking the season’s maximum heat.