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.
Smoke created hazy, orange views in Los Angeles on Saturday as the Sand Fire continued to rage less than 40 miles away from the city's downtown.
Darby will continue to deliver locally heavy rain, gusty winds and rough surf to Hawaii into early Monday. But the tropical storm will provide long-term benefits.
Dangerous heat will surge northward and send temperatures soaring across the northwestern United States during the final week of July.
Much of the eastern United States will continue to swelter with above-average temperatures into the end of the month.
Downpours will spread from the lower Mississippi Valley to eastern and central Texas early this week, delivering needed rain but raising the concern for flash flooding.
With the heat of summer comes many unwelcomed pests, including mosquitoes, ants, fruit flies, wasps and stink bugs, into outdoor spaces and homes.
North Carolina (1975)
Lightning killed 13 cows during a thunderstorm at Kenansville. Heavy rains elsewhere in the state forced the Tar River out of its banks at Greenville, causing 14 families to evacuate their homes.
New York (1975)
Severe thunderstorms in western and central NY: lightning struck a city park in Rochester injuring 12 children, all were playing on a metal jungle gym. One patrolman described the scene as if "someone threw a stick of dynamite in the middle of the crowd and it blew."
Southeastern MA (1990)
Torrential rains: Middleboro 7.20" Bridgewater 5.00" Tauton 4.33" Abington 3.05" Cars were stranded in high water in Fall River, MA.