IRON MOUNTAIN — The region could see thunderstorms tonight and Saturday morning in advance of a heat wave that may be accompanied by high humidity.

The National Weather Service calls for a high near 90 in the Iron Mountain area on Saturday, 95 on Sunday and 90 on Monday.

Thunderstorms are possible again Monday night. The high Tuesday may retreat into the low 70s and only the upper 60s Wednesday.

“A hot and humid airmass is expected over Upper Michigan this weekend into early next week,” NWS forecasters said. “Those sensitive to head, especially those without effective cooling and/or hydration, may be impacted.”

The hot and humid conditions will also support daily thunderstorm chances, forecasters said.

A large bubble of heat is drifting across the U.S. into next week, moving west to east, according to AccuWeather meteorologists.

“With limited days of warmth over the northern Plains, Midwest and Northeast so far this year, the surging heat could catch people off guard as it will be accompanied by some of the most intense sunshine of the year along with high humidity levels,” said AccuWeather’s Alex Sosnowski.

AccuWeather estimates 170 million people will experience temperatures at or above 90 degrees during the heat wave. Temperatures in some areas may climb into the low 100s.

The arrival of the heat wave coincides with the official start of summer. The solstice — or the moment when the Earth’s tilt toward the sun is at its maximum — this year occurs at 9:42 p.m. Central time today.