A dangerous heat wave stretching from Los Angeles to Boston is expected to put more than 100 million Americans under threat this week — and the records have already started falling.

Across the West on Sunday, cities from Utah to Montana logged the hottest temperatures ever measured within their borders. Not the hottest of the summer. The hottest, period.

The Records That Fell Sunday

Salt Lake City hit a preliminary high of 109 degrees, surpassing an all-time record of 107 that had stood since 1960 and been matched in 2002, 2021, and twice in 2022. The city’s temperature records reach back to 1874.

Billings, Montana reached a preliminary 111 degrees, obliterating its previous all-time high of 108 set on July 14, 2002.

Miles City, Montana climbed to a preliminary 115 degrees, breaking its own record of 111 from June 2012.

For perspective, the hottest temperature ever recorded anywhere in Montana is 117 degrees — observed in Medicine Lake in July 1937 and in Glendive in July 1893. Sunday’s readings came uncomfortably close to territory not touched in nearly a century.

A Heat Dome Over the Northern Plains

The driver is a heat dome parked over the Northern Plains, trapping extreme heat and humidity across the country’s northern tier.

Extreme heat warnings are now in effect across a sprawling area from Utah to Michigan’s Upper Peninsula:

• Minneapolis is under warning through Thursday, with a daily heat index reaching 100
• Fargo, North Dakota faces heat indices as high as 110 today and Tuesday
• Duluth, Minnesota and Calumet, Michigan could approach 100
• Detroit is under an extreme heat watch for Tuesday, with a heat index near 107

Out West, Zion Canyon in Utah could feel like 110 degrees today, while Salt Lake City and Billings again push past 100.

The Northeast Is Next

A heat wave arrives in the Northeast on Tuesday, delivering three or more consecutive days above 90 degrees for New York City, Philadelphia, and Washington, D.C.

Heat advisories cover much of the region for at least Tuesday and Wednesday, with heat indices around 100.

The timing splits by geography:

• Tuesday hits the upper Northeast hardest — heat indices of 100 to 104 from Rochester through Albany to Boston
• Wednesday shifts the peak south — near 100 in New York City and around 105 in Washington

Southern California Under Alert

Heat alerts remain in place through Thursday across Southern California.

Coastal valleys will sit between 85 and 90 degrees, while interior valleys climb to 105 through Tuesday.

Conditions worsen midweek. By Wednesday and Thursday, downtown Los Angeles is expected to reach the mid to upper 90s, with interior valleys again touching 105.

Severe Storms Threaten Northern New England

Extreme heat rarely exits quietly.

As a cold front sinks down from Canada and collides with the trapped heat and humidity, northern New England faces a significant severe weather threat Tuesday.

Forecasters have issued a level 3 of 5 risk, warning of:

• Destructive winds exceeding 70 mph
• Hail larger than ping pong balls
• The possibility of a strong tornado or two

The risk zone runs from northeast New York through northern Vermont, northern New Hampshire, and northern Maine. Communities in the path include Burlington and Colchester in Vermont; Plattsburgh and Massena in New York; and Caribou, Maine.

Storms are most likely to fire after 5 p.m. Eastern and persist into the night as the front pushes southward.

What This Means

The scale here is what stands out. This is not a regional event. Roughly a third of the country is facing heat that public health officials classify as dangerous, simultaneously, across radically different climates.

Records set in 1937 and 1893 are being tested. Records set in 2022 have already fallen.

For anyone in the affected zones, the standard advice applies with unusual urgency: limit outdoor exertion during peak afternoon hours, stay hydrated, check on elderly neighbors, and never leave people or pets in parked vehicles.