Monday 10 a.m.
Cooler air advanced from the Great Lakes to the Middle and North Atlantic states during the weekend. The high pressure area marking the center of the cool air mass is moving toward the Carolinas now, and a return southwesterly flow will sponsor a warmup until the next cold front arrives. That flow should be on a line from central New England to southern Illinois on Wednesday, and it will drift southward and stall on a line from North Carolina to southern Missouri on Thursday.
Some showers will accompany the front, and some rain may break out on the north side of it later in the week. At the end of the week and into the weekend, there is quite a variation in model solutions, with some suggesting rain spreads across the Middle Atlantic states then into New England during the weekend.
The dominant cloud type in the summertime is the cumulus. Cumulus clouds can still grow in the fall and winter, but there is less solar heating, and thus less fuel to get these clouds to grow. The clouds in this picture are not associated just with fall, but in summer the same situation would lead clouds with greater vertical development.
...after all that, the point is that zone will be north of most of the eastern half of the country. It will be very warm to hot south of the jet stream. However, weakening cold fronts can advance south of the jet stream. then return north as the next disturbance in the flow approaches.
Yesterday, the temperature hit 92 at Newark, New Jersey, and 90 in Boston. The following map shows a northerly flow affecting the Northeast today, and so it will be noticeably cooler and less humid.
This map shows lightning strokes from 8 a.m. ET yesterday through 7:54 a.m. ET today. There was quite a bit of it in Utah, Colorado, New Mexico and Arizona. For the whole map, 156,172 lightning strokes were recorded.
Looking at the west-to-east upper air flow over New England well ahead of the storm, it seems like the hurricane should stay out at sea, However, as we look through the series of maps, we see the upper-air flow congealing into a strong eastern trough that helped the storm to come right up the coast instead of heading out to sea.
On this satellite picture, we can see the basically dry weather in the Eastern states. The cold front that will ease the midweek heat in the Northeast is shown by the band of thunderstorms in the Midwest. The thunderstorms may weaken and become more scattered as the front comes into the Northeast.
A storm in the tropical Atlantic is being observed for possible strengthening. This map shows the variety of models purporting to show where the center will go. Most solutions suggest it stays well offshore, but you will notice a few outliers suggesting more threat.