5 Numbers to Know About the Coming Heat Wave

Stifling conditions are forecast to spread this week over the eastern half of America — and linger for days.

Millions of Americans from Texas to Maine will face sweltering conditions this week as a heat wave takes hold in the eastern half of the United States, according to forecasters. Beginning Sunday, rising temperatures will hit the South, then stretch over the Midwest before spreading to the East Coast by midweek.

It’s not officially summer yet, so the real baking season is still to come. But this earlier stretch of stifling weather, and the fact that it is expected to linger for days, may be jarring for many regions.

Here are five numbers to help put this coming heat wave — and our warming climate — in context.

The expected high temperature in Fahrenheit on Wednesday in Pittsburgh. It would be the highest ever recorded there during the month of June, said Josh Weiss, a meteorologist with the National Weather Service’s Weather Prediction Center. (In Pittsburgh, he added, there are temperature records dating back to 1875.)

That figure would be just one of what Mr. Weiss said could be dozens of temperature records broken this week in cities across the northeastern United States. On Monday, he said, there are about 20 daily record high temperatures predicted for the Ohio Valley.

And from Tuesday to Thursday, he said, as many as 75 record highs — both daily and for the month — are expected, as the heat wave moves through the Mid-Atlantic through New England. In many of those places, temperatures are expected to exceed 95 degrees sometime in the middle of the week.