When will the heat wave ease in the East?

While another surge of heat and high humidity will be felt in the East this week, cooler and less humid air will fight its way in from Canada in stages through the end of June.

Changes are in the works to give more people in the northeastern third of the United States a break from the excessive heat and humidity this week. The heat, which broke in parts of the Northeast by Monday, will fight back, but millions from the Great Lakes to the mid-Atlantic will get some relief by the end of the week, AccuWeather meteorologists say.

A wedge of cooler and less humid air from eastern Canada produced a marked temperature contrast on Saturday from eastern New England to the mid-Atlantic region. Temperatures were no higher than the 60s in eastern New England, while highs were well into the 90s from New York City to the Ohio Valley and mid-Atlantic regions. Temperatures reached 100 in Washington, D.C.

Following the passage of a cool front, which sparked severe thunderstorms on Sunday afternoon, temperatures and humidity levels were shaved from the Great Lakes to the central Appalachians and the mid-Atlantic into Monday night.

Many people over the interior Southeast, such as in Atlanta and Charlotte will notice a drop in humidity levels by Tuesday with a slight drop in temperature as well. Strong Southern U.S. sunshine by day will quickly negate the cooling effects, however.

Although the air in the wake of the front will still be warm for late June, it will be less extreme than in prior days. As an exception, portions of New England will be substantially warmer, with much less influence from the chilly Atlantic, compared to part of the weekend.

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Meanwhile, a new cool front will gather strength and momentum over south-central Canada and the northern Plains on Tuesday.

Ahead of this front, a south-to-southwesterly flow of air will pump temperatures and humidity levels once again from the Midwest to the East from later Tuesday to Wednesday.

As has been the case with the heat wave in recent days, the biggest spike in temperature and humidity levels will be in the East, rather than the Midwest. Temperatures will peak within a few degrees of 100 from eastern Virginia to Maryland, Delaware, southeastern Pennsylvania and New Jersey on Wednesday.

But, in the wake of the front, temperatures will be slashed by 10-15 degrees by Thursday from the Great Lakes to the mid-Atlantic and New England.

This second batch of cool air will produce highs in the 70s around the Great Lakes and central Appalachians to the 80s in the Ohio Valley and along the mid-Atlantic and New England coasts. A further dip in temperature will continue in the Northeast on Friday.

The change from the oppressive heat and humidity will seem refreshing for millions and some folks from the Great Lakes to the Northeast may be able to shut off the air conditioners and open the windows for a time. But, even over the interior Southeast, a drop in humidity levels can make for comfortable conditions for outdoor plans during the evening and morning hours.

Despite the waves of cooler and less humid air from the Midwest to the Northeast in the coming days, temperatures should not get low enough to inhibit outdoor warm weather activity, such as swimming and ball games. The transition, however, may spark a round of heavy, gusty and locally severe thunderstorms. Similar situations in the past have triggered damaging wind and flash flooding events.

Additional cool fronts are forecast to slice from the Upper Midwest to the Northeast states in early July. While their influence may not be as pronounced as that of the front late this week, it should keep excessive heat limited to a day or so before another slash occurs.

Heat will build over the Western and Central states into July and may attempt to surge back into the Northeast around Independence Day.

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