After high pressure builds into New England today, a trough will cross the region starting tonight. This system will bring a period of beneficial rain and usher in a cooler, more October-like air mass into the region. An upper-level system will pass well to the north of New England, dragging its fronts across the region. This may spawn a surface low near New England, which would help create more widespread showers. These showers will move west east starting Sunday night for western New England and moving eastward through the day Monday.
Showers associated with the cold front will enter into western New England late tonight, likely around midnight. Showers will continue to move eastward at a decent clip through the night. By sunrise, the main batch of rain will have likely moved out of Vermont and into New Hampshire, Maine, eastern Massachusetts and Rhode Island. The formation of the surface low at the system's triple point (where the warm, cold and occluded front meet) will allow for showers to become more widespread as they push eastward.
HRRR showing potential weather just after midnight (1st image) and around mid-morning (2nd image):
Much of New England will see a gradual drying trend heading into the afternoon hours. There will be plenty of instability leftover, so scattered showers will likely pop up around the region, but the more widespread rains will have generally moved on by the afternoon.
HRRR showing potential weather Monday mid-afternoon:
The exception will be eastern Maine, who will see the bulk of rainfall through much of the day Monday and into Monday night. The upper level-low will be to the northeast of New England through Wednesday morning, which will allow for showers to linger in eastern Maine on Tuesday while everyone else generally stays dry.
When all is said and done with this one, a widespread 0.25-0.75 inches of rain will have fallen across New England. With expanding dry conditions over New England, this will be a beneficial dousing. Some heavier downpours and rumbles of thunder will be possible. Where this occurs, a bit more rain is likely, up to 1.5 inches locally. With the upper-low hanging around eastern Maine, they will see the most through midweek. The progressive nature of the front will be the main limiting factor for rainfall amounts.
Once this system passes, New England will remain in a trough as an expansive ridge builds across the western and central United States. This will be a transition away from the country's recent pattern, which has been more of a zonal flow, which is when the jet stream lays generally flat across the country.
This change will mainly be felt with temperatures. Cool weather will prevail for much of next week with widespread highs in the 50s to low 60s. Overnight lows may drop into the 30s to low 40s across New England around midweek. The first chance for a more widespread frost will come during this time. So far, Essex County in Vermont is the only county to have seen a frost advisory this season. That should be changing around mid-week. With unsettled weather persisting in the mountains, some summit snow showers will be possible.
The western ridge will be persistent, with a high chance of above average temperatures across the western two thirds of the country over the next couple weeks. This will keep the east coast in more of a trough. The Climate Prediction Center's 6-10 and 8-14 day outlooks continue to look similar to each other. This pattern will support very standard October weather in New England, as seen in these outlooks, which favors seasonable temperatures and near normal precipitation for New England.
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