United States

By Alex Sosnowski, Expert Senior Meteorologist

June 21, 2012; 7:10 PM

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As heat reaches its peak in the East through Thursday, the clock is ticking on the arrival of cooler, less humid air for the region.

The pattern of cool air rolling out of Canada during recent weeks will soon resume.

Just when you thought summer was here to stay, a cool front will push into the Appalachians and New England during Friday, then to the mid-Atlantic coast by Saturday.

During the transition, thunderstorms are likely to erupt.

While far from a blast of cool air, the first push from Canada will take the edge off the heat and replace dangerous conditions with levels that are much less troublesome. High temperatures in the 90s to near 100 will be replaced by high temperatures in the 80s.

However, the atmosphere will not stop there. More air will flow southeastward from central Canada, and by the middle of next week, temperatures could be running 10 to 15 degrees below normal. This would put highs in the 60s to lower 70s.

Some cooler air will also spill into part of the South next week.

The jet stream, which is a belt of strong steering winds high in the atmosphere, is forecast to take another big southward dip into the Great Lakes and Eastern states next week.

If it rains in some areas during part of the pattern, which is possible in part of the Appalachians and Atlantic Seaboard, daytime highs could be even more off the mark.

The sunny versus rainy weather during the first part of next week may be contingent on the movement of a tropical system, which has yet to be born in the Gulf of Mexico or western Caribbean.

The feature could draw rain and humid conditions up the coast for a time, followed by windy, chilly air from the northwest.

At any rate, after the blast of heat moves away late this week, there is no sign of 95- to 100-degree air returning any time soon for the region.

The first and middle phases of the pattern are not likely to bring much rain to needy areas of the Ohio and middle Mississippi valleys. It is possible that moisture will begin to feed into these areas late in the month from the northern Rockies and central Plains.

Until the first front arrives, tens of millions of people will continue to swelter in a dangerous blast of high heat and humidity that few are accustomed to.