The refreshing end to the weekend will not hold this week in the northeastern United States as steamy air makes a comeback and yields a heat wave in the mid-Atlantic and Ohio Valley.

As quick 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, especially southern areas, on Monday. The steamy air will hold off until Tuesday to return to New England.

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

“There will be a huge difference in how this week will be perceived between the Great Lakes/Northeast and the 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 Ohio Valley and mid-Atlantic, it is the heat wave.”

As humidity levels soar early this week, the number of communities registering highs in the 90s will also increase from the Ohio Valley to the mid-Atlantic Monday into Tuesday.

On Tuesday, highs in the middle 90s will be common from Philadelphia to Baltimore and Richmond, Virginia, as well as in Louisville, Kentucky.

Washington, D.C., will flirt with Tuesday's record high of 99 F from 1988. Temperatures in St. Louis will climb to near the century mark.

Temperatures will then continue to soar into the 90s in these cities and surrounding areas through at least Thursday. More records highs will be challenged, and the hottest communities will be near 100 F.

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

The humidity will push AccuWeather RealFeel® Temperatures to dangerously higher levels.

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 stroke.

Residents will once again be cranking up air conditioners and heading to local pools and lakes to seek relief from the heat. Afternoon sea breezes will help to hold the heat at bay at the beaches.

While the heat wave unfolds to the south, residents from New York City to Pittsburgh, Detroit, Chicago and Indianapolis will not be basking in pleasant conditions this week. Sweltering humidity will have a firm grip on this corridor.

“These areas will not be excessively hot, but you do not get a break at night,” Andrews said. Energy demand will remain high as residents will need air conditioners and fans to sleep comfortably.

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

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