A large-scale upper level low pressure system continues to cycle through the Great Lakes today. This has spawned a surface low well to the south of New England this morning. This surface low will drive New England's rainfall over the next few days. The system will remain to the south of New England for most of today before slowly swinging north this evening. This slow progress of the low means northern New England will be slow to see steadier rain arrive today.

Thursday will have a washout feel across southern New England as periods of rain will continuously rotate through the area throughout the day. Despite this, it won't be raining at the same intensity all day long. Rainfall rates will ebb and flow through the day as waves of showers and downpours move through. Much of northern New England will see more patchy, lighter showers until steadier bouts of rain arrive later in the day.
Below: HRRR showing potential weather early this afternoon (1st image) and this evening (2nd image):
Heading into the evening and overnight hours tonight, the low pressure to the south of New England will become rather elongated as it slowly moves northward into southern New England. Rain will continue to cycle through in the overnight hours.
Below: HRRR showing potential weather overnight Thursday to Friday:

By Friday morning, the system will retrograde westward into New York and Pennsylvania as it gets captured by the upper-level low, where it will remain for much of the day. Another disturbance will likely begin to work up the coast later in the day.

Friday morning should see a pronounced dry slot work into most of New England. Showers activity will become much more isolated during this time. Breaks of sun will even be possible during this time. Colder air will also begin to circulate into New England, allowing some of the showers overnight Thursday and into Friday to become snow showers in the Berkshires, Greens and Whites before precipitation begins to taper.
The exception to this dry slot will be northern and eastern Maine, where the initial batch of steadier rainfall will finally arrive along the system's decaying front. It will likely end up raining much of the day on Friday for a good portion of Maine, which will largely miss out on the action on Thursday.
Below: HRRR showing potential weather Friday morning:

Heading into Friday afternoon, there continues to be indications of a secondary disturbance riding up the coast, offshore of New England. We mentioned this possibility yesterday, but noted the high level of uncertainty. This secondary disturbance continues to look like it will rotate another round of more widespread showers into New England in the afternoon and push northward in the evening.
The exact placement of where this wave of showers ends up remains a struggle to determine. It will be very finicky as it works up the coast. The best chance of seeing another round of widespread rain will be across eastern areas with more scattered and light shower activity farther inland. Should this round of rainfall remain largely offshore, 36 hour rainfall totals for Thursday to Friday will be lighter than expected.
Below: HRRR showing potential weather Friday late afternoon:

While a pronounced easterly flow off the ocean will generally keep precipitation on the wet and mild side, there will be an increasing chance for frozen precipitation in the higher elevations as the system goes on and colder air gradually filters into the region. Depending on how far inland showers can get Friday afternoon and evening, snow showers will be possible across the Greens, Berkshires and Whites once again. Very little to no accumulation is expected below 1,500 feet, though snow could mix in as low as 1,000 feet.
This long duration storm will truck on into Saturday as everything is very slow to pull away in this blocking pattern. Overall, trends have been toward a slower exit this weekend, which we did mention was a distinct possibility this past Monday. Continued showers will be possible region-wide on Saturday, but will likely become more isolated from west to east. Much of Maine could see another mainly wet day.

The final leg of this system will come Saturday afternoon through Sunday morning. Much of New England should be on a drying trend by this time, but remaining showers over northern Maine and northern New Hampshire may gradually mix with or switch over to snow showers during this time. Some accumulations will be possible near the entire New England-Canadian border during this leg.
Overall, New England continues to look at a solid half an inch to inch and a half of rainfall through Friday night. A majority of this will come in two waves, through the day on Thursday and Friday afternoon and evening. For Maine, these waves will come on Thursday night to Friday and Saturday.
A mild flow off the ocean will keep snow a very low impact during this event, with only the mountains seeing much snowfall. The Green and White mountains could see several inches of snow with very little accumulations making it below 1,500 feet. The exception will be near the Canadian border, where a few inches will be possible by Sunday morning.
Below: Probability of snow accumulating at least two inches by Sunday morning:

The system should just about clear out for all but the mountains by Sunday. New England's pattern has shifted to a much more active one heading into the week of Thanksgiving. A northern stream will swing through around Tuesday, bringing another round of showers and potentially high elevation snow showers. This system looks rather meager with limited moisture. Another system could swing through late in the week. We'll have a Thanksgiving week weather outlook posted this evening.
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