Having already overstayed its welcome across much of the southern United States, this summer’s unwelcome extreme heat is invading the Northern Plains and Upper Midwest this holiday weekend before it scorches the Mid-Atlantic and Northeast through midweek. High-temperature records could be tied or broken in many places, including Minneapolis, Green Bay, Wis., Chicago, Detroit, Philadelphia, Raleigh, N.C., and D.C., as the heat persists in some areas well beyond Labor Day, which is typically considered the unofficial end of summer.

As extreme heat expands northward from what has been its home base in the southern United States since June, the number of people who may be exposed to heat requiring extreme caution will surpass 200 million by Labor Day, according to The Washington Post’s heat tracker. Such heat is most dangerous for infants and children up to 4 years old, adults 65 years and older, and people who are overweight, ill or taking certain medications.

Fortunately, the humidity will be lower than it was during the monumental heat wave in the central United States in late August, when heat indexes in the Midwest reached near and above 110 degrees. In this next round, the heat indexes, which describe how hot the air feels when factoring in the humidity, will be close to the actual air temperature. But those conditions will be quite hot, regardless, with many locations reaching daytime highs in the mid-90s to low 100s through Labor Day, and dipping only into the 70s for overnight lows.

“Heat of this magnitude is unusual for this time of year and will pose a health risk to those without adequate cooling/hydration,” the National Weather Service said. “Take this heat seriously — especially if you plan to spend time outside during the Holiday Weekend or participate in early school year outdoor activities.”

Extreme heat has dominated the nation’s southern tier all summer, occasionally making its way north. Many cities from Texas to Florida recorded their hottest August and summer on record. Hot weather is expected to continue along the Gulf Coast through the coming week, especially in Texas, where most of the state is forecast to reach highs near or above 100, or about 6 to 12 degrees above normal.

Heat builds this weekend in Northern Plains and Midwest

Temperatures are likely to soar to near or more than 20 degrees above normal across a large stretch of the Northern Plains and Upper Midwest. Much of Nebraska and South Dakota should experience highs in the upper 90s to low 100s Saturday and Sunday, and in the mid-90s to near 100 on Labor Day. Meanwhile, much of Iowa and Minnesota surges into the 90s today, with highs near 100 in parts of southwest Minnesota on Sunday and Labor Day.

As the heat spreads east, much of Wisconsin and Illinois should reach highs in the low to mid-90s Sunday and Labor Day, with western areas of Wisconsin climbing to the mid- to upper 90s. Much of Michigan, Indiana and Ohio should reach the low 90s Labor Day and Tuesday, with highs in the upper 80s to near 90 on Wednesday.

Some cities that could tie or break temperature records for specific dates include:

• Sioux Falls, S.D., could tie or break its 1956 daily record high for Saturday of 99 degrees. The city’s forecast high for Sunday is near record 100.


• Minneapolis is forecast to reach near 100 degrees Sunday and Labor Day, potentially breaking records of 97 and 98 on Sunday and Monday. With nighttime lows forecast in the mid-70s, the city could also tie or break its daily record for warmest minimum temperature Sunday, Monday and Tuesday.


• Green Bay, Wis., could challenge its daily record high three days in a row. The forecast high is near 95 on Sunday and Monday, both of which would be records. Tuesday is forecast to be slightly cooler, but could still tie or break the record high of 92 observed in 2007. The city could also challenge its daily record for highest minimum temperature Monday and Tuesday.


• Madison, Wis., could likewise challenge its daily record highs for Sunday, Monday and Tuesday. The forecast high is near 95 on Sunday and Monday, which would break the existing record. Tuesday is forecast to a few degrees cooler, but could still flirt with the record high of 93.


• Chicago is expecting a high near 95 on Monday, which could challenge the record high of 95 for the date.


• Detroit is expected to reach the low 90s on Monday, which could tie or break the daily record high of 92.

Nebraska and South Dakota should cool off to highs in the 80s and 70s Tuesday through Friday, with a cooling trend starting Tuesday for Iowa and Minnesota. Temperatures in Wisconsin and Illinois drop slightly by Tuesday, although many spots could still reach the low 90s, before cooling down to the 80s and 70s by Wednesday. Michigan, Indiana and Ohio should observe highs dropping to the 80s and 70s by Thursday.

Mid-Atlantic heat arrives Sunday, could last several days

Temperatures are predicted to climb nearly 15 degrees above normal across parts of the Mid-Atlantic. Much of Northern Virginia, Maryland and southern Pennsylvania, including the Washington area, is forecast to heat up into the low to mid-90s on Sunday. Those areas could surge to the mid- to upper 90s Labor Day through at least midweek, while the low to mid-90s expand south into much of southern Virginia and North Carolina.

Even Delaware and New Jersey briefly warm to the low to mid-90s on Monday, followed by highs near 90 through much of the week.

Some cities that could tie or break temperature records for specific dates include:

• D.C. is forecast to reach near 95 Monday and Tuesday, probably just shy of record highs. At Dulles Airport, in the suburbs west of Washington, both Monday and Wednesday have a chance to tie or break the daily record for highest nighttime lows.


• Baltimore is also expected to top out near 95 Monday and Tuesday — very close to records on both days.


• Philadelphia is forecast to reach near 95 on Monday and Tuesday, near or above existing records.


• Raleigh, N.C., could come close to its daily record high on Tuesday, with a forecast high of 95.

Models suggest that high temperatures in the Mid-Atlantic will remain in the 90s through at least Thursday and possibly Friday. Slightly cooler air could arrive by next weekend, although forecast confidence decreases that far in advance.