Southwesterly breezes will bring warmer air to the I-95 corridor today. Temperatures will approach 70 in Boston and 80 in Washington, D.C. However, a cold front from the eastern Great Lakes will move east to cause showers and even thunderstorms before moving off the East coast tonight. Tomorrow's temperatures will be about 15 degrees lower than today's in the Northeast Corridor, and with the wind increasing, there will be a noticeable chill in the air.
In eastern New England, a low pressure area may develop then strengthen along the cold front. This would prolong the rain tomorrow in Boston and Portland while causing showers in some areas farther west and south. In New York state, it may be cold enough for snow showers in the higher elevations.
Warmer air will take a run at the Northeast toward the end of the week. It is likely to run into resistance in upstate New York and New England, resulting in showers. Farther south, there could be a few showers but Saturday's temperatures between Philadelphia and D.C. could reach 75-80. This video has more:
Looking at the upper-air pattern, it looks wavy but there has been regular progression. This means weather systems keep moving along. However, most models, and especially the ECMWF (European Model), show the pattern amplifying to the point where there are slow-moving storms separated by slow-moving high pressure areas. When you look at the sequence of upper air forecast maps below, you see this evolution.
In fact, at one point, the pattern twists into a shape like the Greek letter Omega. Omega blocks are known for causing long periods of whatever kind of weather you had when the block was being established. In other words, if it was rainy, you were in for more (perhaps a lot). If it was sunny, you could expect a series of sunny days, and drought became a possibility. In the coming setup, it looks like at least several days of showery, cooler-than-average weather across much of the Great Lakes and Northeast next week.
This map is the forecast for Thursday afternoon:
This map is for next Monday afternoon (you should be able to see the Omega shape).
In this map for next Thursday, the Omega pattern is forecast to have broken up, but that leaves a trough dragging slowly into the East with coolness and dampness.
This map shows where Hurricane Joaquin was just before 8 a.m. ET. You can also see the stripe of clouds centered just of the Middle and North Atlantic coasts.
There are competing forces acting on it, and each move it makes will place it under different influences. This has made it very difficult for computer models and meteorologists to judge where it will actually go. This is reflected in the track model collection on this map:
In assessing the final impact of the storm system coming into the East, there are three main components. First is the cold front coming across the Appalachians tonight in a very rich moisture field with ...
On this map, the cold front that will eventually move through the Northeast is in the far northwest corner of the picture. There are areas of showers moving northeastward well ahead of the front, but the steadiest rain is not likely until the cool air moves in and the front stalls.
The Midwest and Northeast are in the latitude zone where winds are primarily from the west. The direct opposite is the case today, as seen on this pressure analysis. The easterly flow brings in moisture from the Atlantic.
The infrared satellite picture below shows the cloudiness as of midmorning on Thursday. If it stays the way it is now, there is no problem in the Northeast. However, on another screen I have been watching the whole area expanding north and west, as indicated on the map.