In contrast to the refreshing air that graced the Northeast this past weekend, steamy air will make a comeback and yield a heat wave in the mid-Atlantic and middle Mississippi Valley this week.

Energy demand will ramp up as people will need air conditioners and fans to sleep comfortably. People will be seeking relief from the heat by visiting local pools and lakes.

As quickly as the less humid air poured into the northeastern United States on Sunday, a shift in the wind will open the door for heat and humidity to build back early this week.

Humidity levels will increase throughout the Great Lakes and mid-Atlantic.

While the spike in humidity will only be temporary in northern areas such as Boston, no relief will come to much of the mid-Atlantic and the middle Mississippi and lower Ohio valleys into late week.

“There will be a huge difference in how this week will be perceived between the Great Lakes/Northeast versus the lower Ohio Valley/mid-Atlantic,” AccuWeather Meteorologist Jim Andrews said.

“Toward the north, there will be no lasting heat, and residents will be dodging thunderstorms,” he said. “Then in the lower Ohio Valley and mid-Atlantic, there will be a heat wave.”

As humidity levels soar early this week, the number of communities registering highs in the 90s F will also increase.

Heat exhaustion vs. heatstroke: What are the warning signs and how should you react?

Northeastern US interactive radar

Map: Heat-related watches, advisories

In Washington, D.C., and St. Louis, highs each day through Thursday will range from 94 to 100.

Record highs will be challenged over much of the region. In Washington, D.C., Thursday's record is 100 set in 1954.

Average temperatures peak in July, but highs in the upper 80s to near 90 are more common.

The humidity will push AccuWeather RealFeel® Temperatures to high levels.

"During a portion of the daylight hours, the RealFeel can be 5 to 10 degrees higher than the actual temperature as it factors in not only the actual temperature and humidity but also sunshine intensity, wind and other conditions," according to AccuWeather Senior Meteorologist Alex Sosnowski.

"Conditions this week in from parts of the mid-Atlantic and the lower Ohio and middle Mississippi Valleys on south can be dangerous for those partaking in strenuous activity during the midday and afternoon hours," Sosnowski said.

Be sure to wear light-clothing, drink plenty of water and avoid strenuous activities during the late morning and afternoon hours (the hottest times of the day) to avoid suffering from heat exhaustion or heat stroke.

While the heat wave unfolds to the south, residents from New York City to Pittsburgh, Detroit, Chicago and Indianapolis will not be basking in cool and dry conditions this week.

“These areas will not be excessively hot, but humidity levels will remain high with little relief at night,” Andrews said.

“A thunderstorm can move through to knock back the humidity, but that would only be brief."

Afternoon sea breezes will keep some beaches cooler, but humidity levels will remain high.

The risk for severe thunderstorms cutting into the heat and humidity will be greatest across the Midwest this week.

“In the Northeast, any thunderstorm can turn severe, but most of the thunderstorms this week will produce drenching downpours," Andrews said. Flash flooding could result.

As has been the case the last two weekends, relief may come just in time for the upcoming weekend.

A push of drier and cooler air may sweep the heat and humidity out of the Ohio Valley, Northeast and mid-Atlantic.

Report a Typo