The upper-air flow forecast for this evening shows the trough that helps to support rainfall ahead of the cold front.
After reaching the 80s today from NYC to Boston, it might not be that warm again through much of next week.
A noticeable push of cooler air will spread southward from Ontario and Quebec into the eastern Great Lakes and New England between tomorrow and Saturday.
A cold front from eastern Canada will slide southward along the East coast between late Friday and the end of the weekend. For the area from Philadelphia to Boston, where temperatures will reach the summery 80s each day through Friday, it will mean a noticeable change to cooler weather.
Average high temperatures in Chicago and New York City are in the mid-70s now, but for the next several days, temperatures will run 8-15 degrees above those long-term averages. Supporting this warmth is a flow aloft that originates over the Southwest:
Rain was common in the Northeast this morning, though Boston was still waiting as of 9 a.m. Their summer dry spell has continued.
There will be an increase in warmth and humidity in the Northeast that will not be reversed until the next cold front arrives.
The comfortably cool air mass that reached the Great Lakes and then the Northeast will be replaced by warmer and more humid air tomorrow and Wednesday. The warmup will be reversed just a day or two later.
Somewhat cooler air will reach New England tomorrow, but take until Sunday to have any noticeable effect farther south.
Once the cold front does come through, a new high pressure area will move across the Midwest and then reach the East.